ax_object_cache_impl.cc

/*
 * Copyright (C) 2014, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "third_party/blink/renderer/modules/accessibility/ax_object_cache_impl.h"

#include "base/auto_reset.h"
#include "base/containers/contains.h"
#include "base/memory/scoped_refptr.h"
#include "base/metrics/histogram_macros.h"
#include "base/ranges/algorithm.h"
#include "mojo/public/cpp/bindings/pending_remote.h"
#include "third_party/blink/public/mojom/permissions/permission.mojom-blink.h"
#include "third_party/blink/public/mojom/permissions/permission_status.mojom-blink.h"
#include "third_party/blink/public/mojom/render_accessibility.mojom-blink.h"
#include "third_party/blink/public/platform/task_type.h"
#include "third_party/blink/public/web/web_local_frame_client.h"
#include "third_party/blink/renderer/core/accessibility/scoped_blink_ax_event_intent.h"
#include "third_party/blink/renderer/core/aom/accessible_node.h"
#include "third_party/blink/renderer/core/display_lock/display_lock_utilities.h"
#include "third_party/blink/renderer/core/dom/document.h"
#include "third_party/blink/renderer/core/dom/document_lifecycle.h"
#include "third_party/blink/renderer/core/dom/dom_node_ids.h"
#include "third_party/blink/renderer/core/dom/slot_assignment_engine.h"
#include "third_party/blink/renderer/core/editing/editing_utilities.h"
#include "third_party/blink/renderer/core/editing/markers/document_marker_controller.h"
#include "third_party/blink/renderer/core/events/event_util.h"
#include "third_party/blink/renderer/core/frame/local_frame.h"
#include "third_party/blink/renderer/core/frame/local_frame_client.h"
#include "third_party/blink/renderer/core/frame/local_frame_view.h"
#include "third_party/blink/renderer/core/frame/settings.h"
#include "third_party/blink/renderer/core/frame/web_local_frame_impl.h"
#include "third_party/blink/renderer/core/html/canvas/html_canvas_element.h"
#include "third_party/blink/renderer/core/html/forms/html_input_element.h"
#include "third_party/blink/renderer/core/html/forms/html_label_element.h"
#include "third_party/blink/renderer/core/html/forms/html_opt_group_element.h"
#include "third_party/blink/renderer/core/html/forms/html_option_element.h"
#include "third_party/blink/renderer/core/html/forms/html_select_element.h"
#include "third_party/blink/renderer/core/html/forms/listed_element.h"
#include "third_party/blink/renderer/core/html/html_area_element.h"
#include "third_party/blink/renderer/core/html/html_frame_owner_element.h"
#include "third_party/blink/renderer/core/html/html_head_element.h"
#include "third_party/blink/renderer/core/html/html_image_element.h"
#include "third_party/blink/renderer/core/html/html_object_element.h"
#include "third_party/blink/renderer/core/html/html_plugin_element.h"
#include "third_party/blink/renderer/core/html/html_progress_element.h"
#include "third_party/blink/renderer/core/html/html_script_element.h"
#include "third_party/blink/renderer/core/html/html_slot_element.h"
#include "third_party/blink/renderer/core/html/html_style_element.h"
#include "third_party/blink/renderer/core/html/html_table_cell_element.h"
#include "third_party/blink/renderer/core/html/html_table_element.h"
#include "third_party/blink/renderer/core/html/html_table_row_element.h"
#include "third_party/blink/renderer/core/html_names.h"
#include "third_party/blink/renderer/core/input_type_names.h"
#include "third_party/blink/renderer/core/layout/layout_image.h"
#include "third_party/blink/renderer/core/layout/layout_inline.h"
#include "third_party/blink/renderer/core/layout/layout_text.h"
#include "third_party/blink/renderer/core/layout/layout_view.h"
#include "third_party/blink/renderer/core/layout/ng/inline/ng_abstract_inline_text_box.h"
#include "third_party/blink/renderer/core/layout/ng/table/layout_ng_table.h"
#include "third_party/blink/renderer/core/layout/ng/table/layout_ng_table_cell.h"
#include "third_party/blink/renderer/core/layout/ng/table/layout_ng_table_row.h"
#include "third_party/blink/renderer/core/page/chrome_client.h"
#include "third_party/blink/renderer/core/page/focus_controller.h"
#include "third_party/blink/renderer/core/page/page.h"
#include "third_party/blink/renderer/core/page/page_animator.h"
#include "third_party/blink/renderer/core/style/content_data.h"
#include "third_party/blink/renderer/core/svg/svg_graphics_element.h"
#include "third_party/blink/renderer/core/svg/svg_style_element.h"
#include "third_party/blink/renderer/modules/accessibility/ax_image_map_link.h"
#include "third_party/blink/renderer/modules/accessibility/ax_inline_text_box.h"
#include "third_party/blink/renderer/modules/accessibility/ax_layout_object.h"
#include "third_party/blink/renderer/modules/accessibility/ax_list_box.h"
#include "third_party/blink/renderer/modules/accessibility/ax_list_box_option.h"
#include "third_party/blink/renderer/modules/accessibility/ax_media_control.h"
#include "third_party/blink/renderer/modules/accessibility/ax_media_element.h"
#include "third_party/blink/renderer/modules/accessibility/ax_menu_list.h"
#include "third_party/blink/renderer/modules/accessibility/ax_menu_list_option.h"
#include "third_party/blink/renderer/modules/accessibility/ax_menu_list_popup.h"
#include "third_party/blink/renderer/modules/accessibility/ax_progress_indicator.h"
#include "third_party/blink/renderer/modules/accessibility/ax_relation_cache.h"
#include "third_party/blink/renderer/modules/accessibility/ax_slider.h"
#include "third_party/blink/renderer/modules/accessibility/ax_validation_message.h"
#include "third_party/blink/renderer/modules/accessibility/ax_virtual_object.h"
#include "third_party/blink/renderer/modules/permissions/permission_utils.h"
#include "third_party/blink/renderer/platform/instrumentation/tracing/trace_event.h"
#include "ui/accessibility/ax_common.h"
#include "ui/accessibility/ax_enums.mojom-blink.h"
#include "ui/accessibility/ax_event.h"
#include "ui/accessibility/ax_role_properties.h"
#include "ui/accessibility/mojom/ax_relative_bounds.mojom-blink.h"

// Prevent code that runs during the lifetime of the stack from altering the
// document lifecycle, for the main document, and the popup document if present.
#if DCHECK_IS_ON()
#define SCOPED_DISALLOW_LIFECYCLE_TRANSITION()                               \
  DocumentLifecycle::DisallowTransitionScope scoped(document_->Lifecycle()); \
  DocumentLifecycle::DisallowTransitionScope scoped2(                        \
      popup_document_ ? popup_document_->Lifecycle()                         \
                      : document_->Lifecycle());
#else
#define SCOPED_DISALLOW_LIFECYCLE_TRANSITION()
#endif  // DCHECK_IS_ON()

namespace blink {

namespace {

bool IsInitialEmptyDocument(const Document& document) {
  // Do not fire for initial empty top document. This helps avoid thrashing the
  // a11y tree, causing an extra serialization.
  // TODO(accessibility) This is an ugly special case -- find a better way.
  // Note: Document::IsInitialEmptyDocument() did not work -- should it?
  if (document.body() && document.body()->hasChildren())
    return false;

  if (document.head() && document.head()->hasChildren())
    return false;

  if (document.ParentDocument())
    return false;

  // No contents and not a child document, return true if about::blank.
  return document.Url().IsAboutBlankURL();
}

// Return a node for the current layout object or ancestor layout object.
Node* GetClosestNodeForLayoutObject(const LayoutObject* layout_object) {
  if (!layout_object)
    return nullptr;
  Node* node = layout_object->GetNode();
  return node ? node : GetClosestNodeForLayoutObject(layout_object->Parent());
}

// Return true if display locked or inside slot recalc, false otherwise.
// Also returns false if not a safe time to perform the check.
bool IsDisplayLocked(const Node* node, bool inclusive = false) {
  if (!node)
    return false;
  // The IsDisplayLockedPreventingPaint() function may attempt to do
  // a flat tree traversal of ancestors. If we're in a flat tree traversal
  // forbidden scope, return false. Additionally, flat tree traversal
  // might call AssignedSlot, so if we're in a slot assignment recalc
  // forbidden scope, return false.
  if (node->GetDocument().IsFlatTreeTraversalForbidden() ||
      node->GetDocument()
          .GetSlotAssignmentEngine()
          .HasPendingSlotAssignmentRecalc()) {
    return false;  // Cannot safely perform this check now.
  }
  return DisplayLockUtilities::IsDisplayLockedPreventingPaint(node, inclusive);
}

bool IsDisplayLocked(const LayoutObject* object) {
  bool inclusive = false;
  while (object) {
    if (const auto* node = object->GetNode())
      return IsDisplayLocked(node, inclusive);
    inclusive = true;
    object = object->Parent();
  }
  return false;
}

bool IsActive(Document& document) {
  return document.IsActive() && !document.IsDetached();
}

bool HasAriaCellRole(Element* elem) {
  DCHECK(elem);
  const AtomicString& role_str = elem->FastGetAttribute(html_names::kRoleAttr);
  if (role_str.empty())
    return false;

  return ui::IsCellOrTableHeader(AXObject::AriaRoleStringToRoleEnum(role_str));
}

// Can role="presentation" aka "none" propagate to descendants of this node?
// Example: it propagates from table->tbody->tr->td, making them all ignored.
bool RolePresentationPropagates(Node* node) {
  // Check for list markup.
  if (IsA<HTMLMenuElement>(node) || IsA<HTMLUListElement>(node) ||
      IsA<HTMLOListElement>(node)) {
    return true;
  }

  // Check for <table>.
  if (IsA<HTMLTableElement>(node))
    return true;  // table section, table row, table cells,

  // Check for display: table CSS.
  if (node->GetLayoutObject() && node->GetLayoutObject()->IsTable())
    return true;

  return false;
}

// Return true if whitespace is not necessary to keep adjacent_node separate
// in screen reader output from surrounding nodes.
bool CanIgnoreSpaceNextTo(LayoutObject* layout_object,
                          bool is_after,
                          int counter = 0) {
  if (!layout_object)
    return true;

  if (counter > 3)
    return false;  // Don't recurse more than 3 times.

  auto* elem = DynamicTo<Element>(layout_object->GetNode());

  // Can usually ignore space next to a <br>.
  // Exception: if the space was next to a <br> with an ARIA role.
  if (layout_object->IsBR()) {
    // As an example of a <br> with a role, Google Docs uses:
    // <span contenteditable=false> <br role="presentation></span>.
    // This construct hides the <br> from the AX tree and uses the space
    // instead, presenting a hard line break as a soft line break.
    DCHECK(elem);
    return !is_after || !elem->FastHasAttribute(html_names::kRoleAttr);
  }

  // If adjacent to a whitespace character, the current space can be ignored.
  if (layout_object->IsText()) {
    auto* layout_text = To<LayoutText>(layout_object);
    if (layout_text->HasEmptyText())
      return false;
    if (layout_text->GetText().Impl()->ContainsOnlyWhitespaceOrEmpty())
      return true;
    auto adjacent_char =
        is_after ? layout_text->FirstCharacterAfterWhitespaceCollapsing()
                 : layout_text->LastCharacterAfterWhitespaceCollapsing();
    return adjacent_char == ' ' || adjacent_char == '\n' ||
           adjacent_char == '\t';
  }

  // Keep spaces between images and other visible content.
  if (layout_object->IsLayoutImage())
    return false;

  // Do not keep spaces between blocks.
  if (!layout_object->IsLayoutInline())
    return true;

  // If next to an element that a screen reader will always read separately,
  // the the space can be ignored.
  // Elements that are naturally focusable even without a tabindex tend
  // to be rendered separately even if there is no space between them.
  // Some ARIA roles act like table cells and don't need adjacent whitespace to
  // indicate separation.
  // False negatives are acceptable in that they merely lead to extra whitespace
  // static text nodes.
  if (elem && HasAriaCellRole(elem))
    return true;

  // Test against the appropriate child text node.
  auto* layout_inline = To<LayoutInline>(layout_object);
  LayoutObject* child =
      is_after ? layout_inline->FirstChild() : layout_inline->LastChild();
  if (!child && elem) {
    // No children of inline element. Check adjacent sibling in same direction.
    Node* adjacent_node =
        is_after ? NodeTraversal::NextIncludingPseudoSkippingChildren(*elem)
                 : NodeTraversal::PreviousAbsoluteSiblingIncludingPseudo(*elem);
    return adjacent_node &&
           CanIgnoreSpaceNextTo(adjacent_node->GetLayoutObject(), is_after,
                                ++counter);
  }
  return CanIgnoreSpaceNextTo(child, is_after, ++counter);
}

bool IsLayoutTextRelevantForAccessibility(const LayoutText& layout_text) {
  if (!layout_text.Parent())
    return false;

  const Node* node = layout_text.GetNode();
  DCHECK(node);  // Anonymous text is processed earlier, doesn't reach here.

#if DCHECK_IS_ON()
  DCHECK(node->GetDocument().Lifecycle().GetState() >=
         DocumentLifecycle::kAfterPerformLayout)
      << "Unclean document at lifecycle "
      << node->GetDocument().Lifecycle().ToString();
#endif

  // Ignore empty text.
  if (layout_text.HasEmptyText())
    return false;

  // Always keep if anything other than collapsible whitespace.
  if (!layout_text.IsAllCollapsibleWhitespace() || layout_text.IsBR())
    return true;

  // Will now look at sibling nodes. We need the closest element to the
  // whitespace markup-wise, e.g. tag1 in these examples:
  // [whitespace] <tag1><tag2>x</tag2></tag1>
  // <span>[whitespace]</span> <tag1><tag2>x</tag2></tag1>.
  // Do not use LayoutTreeBuilderTraversal or FlatTreeTraversal as this may need
  // to be called during slot assignment, when flat tree traversal is forbidden.
  Node* prev_node =
      NodeTraversal::PreviousAbsoluteSiblingIncludingPseudo(*node);
  if (!prev_node)
    return false;

  Node* next_node = NodeTraversal::NextIncludingPseudoSkippingChildren(*node);
  if (!next_node)
    return false;

  // Ignore extra whitespace-only text if a sibling will be presented
  // separately by screen readers whether whitespace is there or not.
  if (CanIgnoreSpaceNextTo(prev_node->GetLayoutObject(), false) ||
      CanIgnoreSpaceNextTo(next_node->GetLayoutObject(), true)) {
    return false;
  }

  // If the prev/next node is also a text node and the adjacent character is
  // not whitespace, CanIgnoreSpaceNextTo will return false. In some cases that
  // is what we want; in other cases it is not. Examples:
  //
  // 1a: <p><span>Hello</span><span>[whitespace]</span><span>World</span></p>
  // 1b: <p><span>Hello</span>[whitespace]<span>World</span></p>
  // 2:  <div><ul><li style="display:inline;">x</li>[whitespace]</ul>y</div>
  //
  // In the first case, we want to preserve the whitespace (crbug.com/435765).
  // In the second case, the whitespace in the markup is not relevant because
  // the "x" is separated from the "y" by virtue of being inside a different
  // block. In order to distinguish these two scenarios, we can use the
  // LayoutBox associated with each node. For the first scenario, each node's
  // LayoutBox is the LayoutBlockFlow associated with the <p>. For the second
  // scenario, the LayoutBox of "x" and the whitespace is the LayoutBlockFlow
  // associated with the <ul>; the LayoutBox of "y" is the one associated with
  // the <div>.
  LayoutBox* box = layout_text.EnclosingBox();
  if (!box)
    return false;

  if (prev_node->GetLayoutObject() && prev_node->GetLayoutObject()->IsText()) {
    LayoutBox* prev_box = prev_node->GetLayoutObject()->EnclosingBox();
    if (prev_box != box)
      return false;
  }

  if (next_node->GetLayoutObject() && next_node->GetLayoutObject()->IsText()) {
    LayoutBox* next_box = next_node->GetLayoutObject()->EnclosingBox();
    if (next_box != box)
      return false;
  }

  return true;
}

bool IsHiddenTextNodeRelevantForAccessibility(const Text& text_node,
                                              bool is_display_locked) {
  // Children of an <iframe> tag will always be replaced by a new Document,
  // either loaded from the iframe src or empty. In fact, we don't even parse
  // them and they are treated like one text node. Consider irrelevant.
  if (AXObject::IsFrame(text_node.parentElement()))
    return false;

  // Layout has more info available to determine if whitespace is relevant.
  // If display-locked, layout object may be missing or stale:
  // Assume that all display-locked text nodes are relevant, but only create
  // an AXNodeObject in order to avoid using a stale layout object.
  if (is_display_locked)
    return true;

  // If unrendered + no parent, it is in a shadow tree. Consider irrelevant.
  if (!text_node.parentElement()) {
    DCHECK(text_node.IsInShadowTree());
    return false;
  }

  // If unrendered and in <canvas>, consider even whitespace relevant.
  if (text_node.parentElement()->IsInCanvasSubtree())
    return true;

  // Must be unrendered because of CSS. Consider relevant if non-whitespace.
  // Allowing rendered non-whitespace to be considered relevant will allow
  // use for accessible relations such as labelledby and describedby.
  return !text_node.ContainsOnlyWhitespaceOrEmpty();
}

bool IsShadowContentRelevantForAccessibility(const Node* node) {
  DCHECK(node->ContainingShadowRoot());

  // Return false if inside a shadow tree of something that can't have children,
  // for example, an <img> has a user agent shadow root containing a <span> for
  // the alt text. Do not create an accessible for that as it would be unable
  // to have a parent that has it as a child.
  if (!AXObject::CanHaveChildren(To<Element>(*node->OwnerShadowHost()))) {
    return false;
  }

  // Native <img> create extra child nodes to hold alt text, which are not
  // allowed as children. Note: images can have image map children, but these
  // are moved from the <map> descendants and are not descendants of the image.
  // See AXNodeObject::AddImageMapChildren().
  if (node->IsInUserAgentShadowRoot() &&
      IsA<HTMLImageElement>(node->OwnerShadowHost())) {
    return false;
  }

  // Don't use non-<option> descendants of an AXMenuList.
  // If the UseAXMenuList flag is on, we use a specialized class AXMenuList
  // for handling the user-agent shadow DOM exposed by a <select> element.
  // That class adds a mock AXMenuListPopup, which adds AXMenuListOption
  // children for <option> descendants only.
  if (AXObjectCacheImpl::UseAXMenuList() && node->IsInUserAgentShadowRoot() &&
      !IsA<HTMLOptionElement>(node)) {
    // Find any ancestor <select> if it is present.
    Node* host = node->OwnerShadowHost();
    auto* select_element = DynamicTo<HTMLSelectElement>(host);
    if (!select_element) {
      // An <optgroup> can be a shadow host too -- look for it's owner <select>.
      if (auto* opt_group_element = DynamicTo<HTMLOptGroupElement>(host))
        select_element = opt_group_element->OwnerSelectElement();
    }
    if (select_element) {
      if (!select_element->GetLayoutObject())
        return select_element->IsInCanvasSubtree();
      // Non-option: only create AXObject if not inside an AXMenuList.
      return !AXObjectCacheImpl::ShouldCreateAXMenuListFor(
          select_element->GetLayoutObject());
    }
  }

  // Outside of AXMenuList descendants, all other non-slot user agent shadow
  // nodes are relevant.
  const HTMLSlotElement* slot_element =
      ToHTMLSlotElementIfSupportsAssignmentOrNull(node);
  if (!slot_element)
    return true;

  // Slots are relevant if they have content.
  // However, this can only be checked during safe times.
  // During other times we must assume that the <slot> is relevant.
  // TODO(accessibility) Consider removing this rule, but it will require
  // a different way of dealing with these PDF test failures:
  // https://chromium-review.googlesource.com/c/chromium/src/+/2965317
  // For some reason the iframe tests hang, waiting for content to change. In
  // other words, returning true here causes some tree updates not to occur.
  if (node->GetDocument().IsFlatTreeTraversalForbidden() ||
      node->GetDocument()
          .GetSlotAssignmentEngine()
          .HasPendingSlotAssignmentRecalc()) {
    return true;
  }

  // If the slot element's host is an <object>/<embed>with any descendant nodes
  // (including whitespace), LayoutTreeBuilderTraversal::FirstChild will
  // return a node. We should only treat that node as slot content if it is
  // being used as fallback content.
  if (const HTMLPlugInElement* plugin_element =
          DynamicTo<HTMLPlugInElement>(node->OwnerShadowHost())) {
    return plugin_element->UseFallbackContent();
  }

  return LayoutTreeBuilderTraversal::FirstChild(*slot_element);
}

bool IsLayoutObjectRelevantForAccessibility(const LayoutObject& layout_object) {
  if (layout_object.IsAnonymous()) {
    // Anonymous means there is no DOM node, and it's been inserted by the
    // layout engine within the tree. An example is an anonymous block that is
    // inserted as a parent of an inline where there are block siblings.
    return AXObjectCacheImpl::IsRelevantPseudoElementDescendant(layout_object);
  }

  if (layout_object.IsText())
    return IsLayoutTextRelevantForAccessibility(To<LayoutText>(layout_object));

  // An AXMenuListOption will be created, which is a subclass of AXNodeObject,
  // not of AXLayoutObject.
  if (AXObjectCacheImpl::ShouldCreateAXMenuListOptionFor(
          layout_object.GetNode())) {
    return false;
  }

  // An AXImageMapLink will be created, which is a subclass of AXNodeObject, not
  // of AXLayoutObject.
  if (IsA<HTMLAreaElement>(layout_object.GetNode()))
    return false;

  return true;
}

bool IsSubtreePrunedForAccessibility(const Element* node) {
  if (IsA<HTMLAreaElement>(node) && !IsA<HTMLMapElement>(node->parentNode()))
    return true;  // <area> without parent <map> is not relevant.

  if (IsA<HTMLMapElement>(node))
    return true;  // Contains children for an img, but is not its own object.

  if (node->HasTagName(html_names::kColgroupTag))
    return true;  // Affects table layout, but doesn't get it's own AXObject.

  if (node->IsPseudoElement()) {
    if (!AXObjectCacheImpl::IsRelevantPseudoElement(*node))
      return true;
  }

  if (const HTMLSlotElement* slot =
          ToHTMLSlotElementIfSupportsAssignmentOrNull(node)) {
    if (!AXObjectCacheImpl::IsRelevantSlotElement(*slot))
      return true;
  }

  // <optgroup> is irrelevant inside of a <select> menulist.
  if (auto* opt_group = DynamicTo<HTMLOptGroupElement>(node)) {
    if (auto* select = opt_group->OwnerSelectElement()) {
      if (select->UsesMenuList())
        return true;
    }
  }

  // An HTML <title> does not require an AXObject: the document's name is
  // retrieved directly via the inner text.
  if (IsA<HTMLTitleElement>(node))
    return true;

  return false;
}

// Return true if node is head/style/script or any descendant of those.
// Also returns true for descendants of any type of frame, because the frame
// itself is in the tree, but not DOM descendants (their contents are in a
// different document).
bool IsInPrunableHiddenContainerInclusive(const Node& node,
                                          bool parent_ax_known,
                                          bool is_display_locked) {
  int max_depth_to_check = INT_MAX;
  if (parent_ax_known) {
    // Optimization: only need to check the current object if the parent the
    // parent_ax is already known, because it we are attempting to add this
    // object from something already relevant in the AX tree, and therefore
    // can't be inside a <head>, <style>, <script> or SVG <style> element.
    // However, there is an edge case that if it is display locked content
    // we must also check the parent, which can be visible and included
    // in the tree. This edge case is handled to satisfy tests and is not
    // likely to be a real-world condition.
    max_depth_to_check = is_display_locked ? 2 : 1;
  }

  for (const Node* ancestor = &node; ancestor;
       ancestor = ancestor->parentElement()) {
    // Objects inside <head> are pruned.
    if (IsA<HTMLHeadElement>(ancestor))
      return true;
    // Objects inside a <style> are pruned.
    if (IsA<HTMLStyleElement>(ancestor))
      return true;
    // Objects inside a <script> are true.
    if (IsA<HTMLScriptElement>(ancestor))
      return true;
    // Elements inside of a frame/iframe are true unless inside a document
    // that is a child of the frame. In the case where descendants are allowed,
    // they will be in a different document, and therefore this loop will not
    // reach the frame/iframe.
    if (AXObject::IsFrame(ancestor))
      return true;
    // Style elements in SVG are not display: none, unlike HTML style
    // elements, but they are still hidden along with their contents and thus
    // treated as true for accessibility.
    if (IsA<SVGStyleElement>(ancestor))
      return true;

    if (--max_depth_to_check <= 0)
      break;
  }

  // All other nodes are relevant, even if hidden.
  return false;
}

// -----------------------------------------------------------------------------
// DetermineAXObjectType() determines what type of AXObject should be created
// for the given node and layout_object.
// * Pass in the Node, the LayoutObject or both.
// * Passing in |parent_ax_known| when there is  known parent is an optimization
// and does not affect the return value.
// Some general rules:
// * If neither the node nor layout object are relevant for accessibility, will
// return kPruneSubtree, which will cause no AXObject to be created, and
// result in the entire subtree being pruned at that point.
// * If the node is part of a forbidden subtree, then kPruneSubtree is used.
// * If both the node and layout are relevant, kAXLayoutObject is preferred,
// otherwise: kAXNodeObject for relevant nodes, kLayoutObject for layout.
// -----------------------------------------------------------------------------
AXObjectType DetermineAXObjectType(const Node* node,
                                   const LayoutObject* layout_object,
                                   bool parent_ax_known = false) {
  DCHECK(layout_object || node);
  bool is_display_locked =
      node ? IsDisplayLocked(node) : IsDisplayLocked(layout_object);
  if (is_display_locked)
    layout_object = nullptr;
  DCHECK(!node || !layout_object || layout_object->GetNode() == node);

  bool is_node_relevant = false;

  if (node) {
    if (!node->isConnected()) {
      return kPruneSubtree;
    }

    if (node->ContainingShadowRoot() &&
        !IsShadowContentRelevantForAccessibility(node)) {
      return kPruneSubtree;
    }

    if (!IsA<Element>(node) && !IsA<Text>(node)) {
      // All remaining types, such as the document node, doctype node.
      return layout_object ? kAXLayoutObject : kPruneSubtree;
    }

    if (const Element* element = DynamicTo<Element>(node)) {
      if (IsSubtreePrunedForAccessibility(element))
        return kPruneSubtree;
      else
        is_node_relevant = true;
    } else {  // Text is the only remaining type.
      if (layout_object) {
        // If there's layout for this text, it will either be pruned or an
        // AXLayoutObject will be created for it. The logic of whether to return
        // kAXLayoutObject or kPruneSubtree will come purely from
        // is_layout_relevant further down.
        return IsLayoutObjectRelevantForAccessibility(*layout_object)
                   ? kAXLayoutObject
                   : kPruneSubtree;
      } else {
        // Otherwise, base the decision on the best info we have on the node.
        is_node_relevant = IsHiddenTextNodeRelevantForAccessibility(
            To<Text>(*node), is_display_locked);
      }
    }
  }

  bool is_layout_relevant =
      layout_object && IsLayoutObjectRelevantForAccessibility(*layout_object);

  // Prune if neither the LayoutObject nor Node are relevant.
  if (!is_layout_relevant && !is_node_relevant)
    return kPruneSubtree;

  // If a node is not rendered, prune if it is in head/style/script or a DOM
  // descendant of an iframe.
  if (!is_layout_relevant && IsInPrunableHiddenContainerInclusive(
                                 *node, parent_ax_known, is_display_locked)) {
    return kPruneSubtree;
  }

  return is_layout_relevant ? kAXLayoutObject : kAXNodeObject;
}

}  // namespace

// static
bool AXObjectCacheImpl::use_ax_menu_list_ = false;

// static
AXObjectCache* AXObjectCacheImpl::Create(Document& document,
                                         const ui::AXMode& ax_mode) {
  return MakeGarbageCollected<AXObjectCacheImpl>(document, ax_mode);
}

AXObjectCacheImpl::AXObjectCacheImpl(Document& document,
                                     const ui::AXMode& ax_mode)
    : document_(document),
      ax_mode_(ax_mode),
      validation_message_axid_(0),
      active_aria_modal_dialog_(nullptr),
      relation_cache_(std::make_unique<AXRelationCache>(this)),
      accessibility_event_permission_(mojom::blink::PermissionStatus::ASK),
      permission_service_(document.GetExecutionContext()),
      permission_observer_receiver_(this, document.GetExecutionContext()),
      render_accessibility_host_(document.GetExecutionContext()),
      ax_tree_source_(BlinkAXTreeSource::Create(*this)),
      ax_tree_serializer_(std::make_unique<ui::AXTreeSerializer<AXObject*>>(
          ax_tree_source_,
          /*crash_on_error*/ true)) {
  use_ax_menu_list_ = GetSettings()->GetUseAXMenuList();
}

AXObjectCacheImpl::~AXObjectCacheImpl() {
#if DCHECK_IS_ON()
  DCHECK(has_been_disposed_);
#endif
}

// This is called shortly before the AXObjectCache is deleted.
// The destruction of the AXObjectCache will do most of the cleanup.
void AXObjectCacheImpl::Dispose() {
  DCHECK(!has_been_disposed_) << "Something is wrong, trying to dispose twice.";

  // Don't perform expensive computations while tearing down.
  has_been_disposed_ = true;

  // Detach all objects now. This prevents more work from occurring if we wait
  // for the rendering engine to detach each node individually, because that
  // will cause the renderer to attempt to potentially repair parents, and
  // detach each child individually as Detach() calls ClearChildren().
  // TODO(accessibility) We could just remove this method if code that checks
  // HasBeenDisposed()/has_been_disposed_ had another way to check for shutdown.
  for (auto& entry : objects_) {
    AXObject* obj = entry.value;
    obj->Detach();
  }
}

void AXObjectCacheImpl::AddInspectorAgent(InspectorAccessibilityAgent* agent) {
  agents_.insert(agent);
}

void AXObjectCacheImpl::RemoveInspectorAgent(
    InspectorAccessibilityAgent* agent) {
  agents_.erase(agent);
}

AXObject* AXObjectCacheImpl::Root() {
  if (AXObject* root = SafeGet(document_))
    return root;
  return GetOrCreate(document_);
}

AXObject* AXObjectCacheImpl::ObjectFromAXID(AXID id) const {
  auto it = objects_.find(id);
  return it != objects_.end() ? it->value : nullptr;
}

Node* AXObjectCacheImpl::FocusedElement() {
  Node* focused_node = document_->FocusedElement();
  if (!focused_node)
    focused_node = document_;

  // A popup is showing: return the focus within instead of the focus in the
  // main document. Do not do this for HTML <select>, which has special
  // focus manager using the kActiveDescendantId.
  if (GetPopupDocumentIfShowing() && !IsA<HTMLSelectElement>(focused_node)) {
    if (Node* focus_in_popup = GetPopupDocumentIfShowing()->FocusedElement())
      return focus_in_popup;
  }

  return focused_node;
}

void AXObjectCacheImpl::UpdateLifecycleIfNeeded(Document& document) {
  DCHECK(document.defaultView());
  DCHECK(document.GetFrame());
  DCHECK(document.View());

  document.View()->UpdateAllLifecyclePhasesExceptPaint(
      DocumentUpdateReason::kAccessibility);
}

void AXObjectCacheImpl::UpdateAXForAllDocuments() {
#if DCHECK_IS_ON()
  DCHECK(!IsFrozen())
      << "Don't call UpdateAXForAllDocuments() here; layout and a11y are "
         "already clean at the start of serialization.";
  DCHECK(!updating_layout_and_ax_) << "Undesirable recursion.";
  base::AutoReset<bool> updating(&updating_layout_and_ax_, true);
#endif

  // First update the layout for the main and popup document.
  UpdateLifecycleIfNeeded(GetDocument());
  if (Document* popup_document = GetPopupDocumentIfShowing())
    UpdateLifecycleIfNeeded(*popup_document);

  // Next flush all accessibility events and dirty objects, for both the main
  // and popup document.
  if (IsDirty() || HasDirtyObjects())
    ProcessDeferredAccessibilityEvents(GetDocument());
}

AXObject* AXObjectCacheImpl::GetOrCreateFocusedObjectFromNode(Node* node) {
#if DCHECK_IS_ON()
  DCHECK(GetDocument().Lifecycle().GetState() >=
         DocumentLifecycle::kAfterPerformLayout);
  if (GetPopupDocumentIfShowing()) {
    DCHECK(GetPopupDocumentIfShowing()->Lifecycle().GetState() >=
           DocumentLifecycle::kAfterPerformLayout);
  }
#endif

  AXObject* obj = GetOrCreate(node);
  if (!obj)
    return nullptr;

  Settings* settings = GetSettings();
  if (settings && settings->GetAriaModalPrunesAXTree()) {
    // It is possible for the active_aria_modal_dialog_ to become detached in
    // between the time a node claims focus and the time we notify platforms
    // of that focus change. For instance given an aria-modal dialog which was
    // newly unhidden (rather than newly added to the DOM):
    // * HandleFocusedUIElementChanged calls UpdateActiveAriaModalDialog
    // * UpdateActiveAriaModalDialog sets the value of active_aria_modal_dialog_
    //   and then marks the entire tree dirty if that value changed.
    // * The subsequent tree update results in the stored active dialog being
    //   detached and replaced.
    // Should this occur, the focused node we're getting or creating here is
    // not a descendant of active_aria_modal_dialog_ and is thus pruned from
    // the tree. This leads to firing the event on the included parent object,
    // which is likely a non-focusable container.
    // We could probably address this situation in one of the clean-layout
    // functions (e.g. HandleNodeGainedFocusWithCleanLayout). However, because
    // both HandleNodeGainedFocusWithCleanLayout and FocusedObject call
    // GetOrCreateFocusedObjectFromNode, detecting and correcting this issue
    // here seems like it covers more bases.
    // TODO(crbug.com/1328815): We need to take a close look at the aria-modal
    // tree pruning logic to be sure there are not other situations where we
    // incorrectly prune content which should be exposed.
    if (active_aria_modal_dialog_ && active_aria_modal_dialog_->IsDetached())
      UpdateActiveAriaModalDialog(node);
  }

  // the HTML element, for example, is focusable but has an AX object that is
  // ignored
  if (!obj->AccessibilityIsIncludedInTree())
    obj = obj->ParentObjectIncludedInTree();

  return obj;
}

AXObject* AXObjectCacheImpl::FocusedObject() {
  return GetOrCreateFocusedObjectFromNode(FocusedElement());
}

const ui::AXMode& AXObjectCacheImpl::GetAXMode() {
  return ax_mode_;
}

void AXObjectCacheImpl::SetAXMode(const ui::AXMode& ax_mode) {
  ax_mode_ = ax_mode;
}

AXObject* AXObjectCacheImpl::Get(const LayoutObject* layout_object,
                                 AXObject* parent_for_repair) {
  if (!layout_object)
    return nullptr;

  if (Node* node = layout_object->GetNode()) {
    // If there is a node, it is preferred for backing the AXObject.
    DCHECK(!layout_object_mapping_.Contains(layout_object));
    return Get(node);
  }

  auto it_id = layout_object_mapping_.find(layout_object);
  if (it_id == layout_object_mapping_.end()) {
    return nullptr;
  }
  AXID ax_id = it_id->value;
  DCHECK(!WTF::IsHashTraitsDeletedValue<HashTraits<AXID>>(ax_id));

  if (IsDisplayLocked(layout_object) ||
      !IsLayoutObjectRelevantForAccessibility(*layout_object)) {
    // Change from AXLayoutObject -> AXNodeObject.
    // We previously saved the node in the cache with its layout object,
    // but now it's in a locked subtree so we should remove the entry with its
    // layout object and replace it with an AXNodeObject created from the node
    // instead. Do this later at a safe time.
    Remove(const_cast<LayoutObject*>(layout_object));
    return nullptr;
  }

  auto it_result = objects_.find(ax_id);
  AXObject* result = it_result != objects_.end() ? it_result->value : nullptr;
  DCHECK(result) << "Had AXID for Node but no entry in objects_";
  DCHECK(result->IsAXNodeObject());
  // Do not allow detached objects except when disposing entire tree.
  DCHECK(!result->IsDetached() || has_been_disposed_)
      << "Detached AXNodeObject in map: "
      << "AXID#" << ax_id << " LayoutObject=" << layout_object;

  if (result->CachedParentObject()) {
    DCHECK(!parent_for_repair ||
           parent_for_repair == result->CachedParentObject())
        << "If there is both a previous parent, and a parent supplied for "
           "repair, they must match.";
  } else if (parent_for_repair) {
    result->SetParent(parent_for_repair);
  }

  // If there is no node for the AXObject, then it is an anonymous layout
  // object (e.g. a pseudo-element or object introduced to match the structure
  // of content). Such objects can only be created or destroyed via creation of
  // their parents and recursion via AddPseudoElementChildrenFromLayoutTree.
  // RepairMissingParent will not be able to restore a missing parent; instead
  // we should never need to do that.
  DCHECK(!result->IsMissingParent() || !result->GetNode())
      << "Had AXObject but is missing parent: " << layout_object << " "
      << result->ToString(true, true);

  return result;
}

AXObject* AXObjectCacheImpl::SafeGet(const Node* node,
                                     bool allow_display_locking_invalidation,
                                     bool allow_layout_object_relevance_check) {
  if (!node)
    return nullptr;

#if DCHECK_IS_ON()
  if (const Element* element = DynamicTo<Element>(node)) {
    if (AccessibleNode* accessible_node = element->ExistingAccessibleNode()) {
      DCHECK(!accessible_node_mapping_.Contains(accessible_node))
          << "The accessible node directly attached to an element should not "
             "have its own AXObject: "
          << element;
    }
  }
#endif

  auto iter = node_object_mapping_.find(node);
  if (iter == node_object_mapping_.end()) {
    return nullptr;
  }

  AXID node_id = iter->value;
  auto it_result = objects_.find(node_id);
  if (it_result == objects_.end()) {
    return nullptr;
  }

  AXObject* result = it_result->value;
  DCHECK(result) << "AXID#" << node_id
                 << " in map, but matches an AXObject of null, for " << node;

  // When shutting down, allow detached nodes to be in the map, and do not
  // attempt invalidations.
  if (has_been_disposed_) {
    return result->IsDetached() ? nullptr : result;
  }

  DCHECK(!result->IsDetached()) << "Detached object was in map.";

  // Compute whether an allowed invalidation is necessary that alter whether the
  // current object should be an AXLayoutObject vs AXNodeObject.
  bool is_ax_layout_object = IsA<AXLayoutObject>(result);
  bool should_be_ax_layout_object = is_ax_layout_object;
  if (node->GetLayoutObject()) {
    if (allow_display_locking_invalidation) {
      // Nodes that are display locked may have stale layout objects. We enforce
      // that they use AXNodeObject because the layout is not up-to-date.
      should_be_ax_layout_object = !IsDisplayLocked(node);
    }
    if (should_be_ax_layout_object && allow_layout_object_relevance_check &&
        !IsLayoutObjectRelevantForAccessibility(*node->GetLayoutObject())) {
      should_be_ax_layout_object = false;
    }
  }

  // Process any computed invalidation, queuing the work for later.
  // TODO(crbug.com/1380449) Replace this system with notifications that
  // invalidate based on Blink's knowledge of what's changing, instead of
  // checking objects when we touch them.
  if (is_ax_layout_object != should_be_ax_layout_object) {
    Invalidate(node->GetDocument(), result->AXObjectID());
  }

  return result;
}

AXObject* AXObjectCacheImpl::Get(const Node* node) {
  return SafeGet(node, /* allow_display_locking_invalidation */ true,
                 /* allow_layout_object_relevance_check */ true);
}

AXObject* AXObjectCacheImpl::Get(NGAbstractInlineTextBox* inline_text_box) {
  if (!inline_text_box)
    return nullptr;

  auto it_ax = inline_text_box_object_mapping_.find(inline_text_box);
  AXID ax_id =
      it_ax != inline_text_box_object_mapping_.end() ? it_ax->value : 0;
  DCHECK(!WTF::IsHashTraitsDeletedValue<HashTraits<AXID>>(ax_id));
  if (!ax_id)
    return nullptr;

  auto it_result = objects_.find(ax_id);
  AXObject* result = it_result != objects_.end() ? it_result->value : nullptr;
#if DCHECK_IS_ON()
  DCHECK(result) << "Had AXID for inline text box but no entry in objects_";
  DCHECK(result->IsAXInlineTextBox());
  // Do not allow detached objects except when disposing entire tree.
  DCHECK(!result->IsDetached() || has_been_disposed_)
      << "Detached AXInlineTextBox in map: "
      << "AXID#" << ax_id << " Node=" << inline_text_box->GetText();
#endif
  return result;
}

void AXObjectCacheImpl::Invalidate(Document& document, AXID ax_id) {
  if (GetInvalidatedIds(document).insert(ax_id).is_new_entry)
    ScheduleAXUpdate();
}

AXID AXObjectCacheImpl::GetAXID(Node* node) {
  AXObject* ax_object = GetOrCreate(node);
  if (!ax_object)
    return ui::AXNodeData::kInvalidAXID;
  return ax_object->AXObjectID();
}

AXID AXObjectCacheImpl::GetExistingAXID(Node* node) {
  AXObject* ax_object = SafeGet(node);
  if (!ax_object)
    return ui::AXNodeData::kInvalidAXID;
  return ax_object->AXObjectID();
}

AXObject* AXObjectCacheImpl::Get(AccessibleNode* accessible_node) {
  if (!accessible_node)
    return nullptr;

  if (accessible_node->element()) {
    DCHECK(!accessible_node_mapping_.Contains(accessible_node))
        << "The accessible node directly attached to an element should not "
           "have its own AXObject: "
        << accessible_node->element();
    // When the AccessibleNode is attached to an element, return the element's
    // accessible object instead.
    return SafeGet(accessible_node->element());
  }

  auto it_ax = accessible_node_mapping_.find(accessible_node);
  AXID ax_id = it_ax != accessible_node_mapping_.end() ? it_ax->value : 0;
  DCHECK(!WTF::IsHashTraitsDeletedValue<HashTraits<AXID>>(ax_id));
  if (!ax_id)
    return nullptr;

  auto it_result = objects_.find(ax_id);
  AXObject* result = it_result != objects_.end() ? it_result->value : nullptr;
#if DCHECK_IS_ON()
  DCHECK(result) << "Had AXID for accessible_node but no entry in objects_";
  DCHECK(IsA<AXVirtualObject>(result));
  // Do not allow detached objects except when disposing entire tree.
  DCHECK(!result->IsDetached() || has_been_disposed_)
      << "Detached AXVirtualObject in map: "
      << "AXID#" << ax_id << " Node=" << accessible_node->element();
#endif
  return result;
}

AXObject* AXObjectCacheImpl::GetAXImageForMap(HTMLMapElement& map) {
  // Find first child node of <map> that has an AXObject and return it's
  // parent, which should be a native image.
  Node* child = LayoutTreeBuilderTraversal::FirstChild(map);
  while (child) {
    if (AXObject* ax_child = SafeGet(child)) {
      if (AXObject* ax_image = ax_child->CachedParentObject()) {
        if (ax_image->IsDetached()) {
          return nullptr;
        }
        DCHECK(IsA<HTMLImageElement>(ax_image->GetNode()))
            << "Expected image AX parent of <map>'s DOM child, got: "
            << ax_image->GetNode() << "\n* Map's DOM child was: " << child
            << "\n* ax_image: " << ax_image->ToString(true, true);
        return ax_image;
      }
    }
    child = LayoutTreeBuilderTraversal::NextSibling(*child);
  }
  return nullptr;
}

AXObject* AXObjectCacheImpl::CreateFromRenderer(LayoutObject* layout_object) {
  Node* node = layout_object->GetNode();

  // media element
  if (node && node->IsMediaElement())
    return AccessibilityMediaElement::Create(layout_object, *this);

  if (node && node->IsMediaControlElement())
    return AccessibilityMediaControl::Create(layout_object, *this);

  if (IsA<HTMLOptionElement>(node))
    return MakeGarbageCollected<AXListBoxOption>(layout_object, *this);

  if (auto* html_input_element = DynamicTo<HTMLInputElement>(node)) {
    const AtomicString& type = html_input_element->type();
    if (type == input_type_names::kRange)
      return MakeGarbageCollected<AXSlider>(layout_object, *this);
  }

  if (auto* select_element = DynamicTo<HTMLSelectElement>(node)) {
    if (select_element->UsesMenuList()) {
      if (use_ax_menu_list_) {
        DCHECK(ShouldCreateAXMenuListFor(layout_object));
        return MakeGarbageCollected<AXMenuList>(layout_object, *this);
      }
    } else {
      return MakeGarbageCollected<AXListBox>(layout_object, *this);
    }
  }

  if (IsA<HTMLProgressElement>(node)) {
    return MakeGarbageCollected<AXProgressIndicator>(layout_object, *this);
  }

  return MakeGarbageCollected<AXLayoutObject>(layout_object, *this);
}

// Returns true if |node| is an <option> element and its parent <select>
// is a menu list (not a list box).
// static
bool AXObjectCacheImpl::ShouldCreateAXMenuListOptionFor(const Node* node) {
  auto* option_element = DynamicTo<HTMLOptionElement>(node);
  if (!option_element)
    return false;

  if (auto* select = option_element->OwnerSelectElement())
    return ShouldCreateAXMenuListFor(select->GetLayoutObject());

  return false;
}

// static
bool AXObjectCacheImpl::ShouldCreateAXMenuListFor(LayoutObject* layout_object) {
  if (!layout_object)
    return false;

  if (!AXObjectCacheImpl::UseAXMenuList())
    return false;

  if (auto* select = DynamicTo<HTMLSelectElement>(layout_object->GetNode()))
    return select->UsesMenuList();

  return false;
}

// static
bool AXObjectCacheImpl::IsRelevantSlotElement(const HTMLSlotElement& slot) {
  DCHECK(AXObject::CanSafelyUseFlatTreeTraversalNow(slot.GetDocument()));
  DCHECK(slot.SupportsAssignment());

  // Don't use a <slot> inside of an AXMenuList.
  // TODO(accessibility) Remove AXMenuList and follow the shadow DOM.
  if (slot.IsInUserAgentShadowRoot()) {
    if (HTMLSelectElement* select =
            DynamicTo<HTMLSelectElement>(slot.OwnerShadowHost())) {
      if (ShouldCreateAXMenuListFor(select->GetLayoutObject())) {
        return false;
      }
    }
  }

  // HasAssignedNodesNoRecalc() will return false when  the slot is not in the
  // flat tree. We must also return true when the slot has ordinary children
  // (fallback content).
  return slot.HasAssignedNodesNoRecalc() || slot.hasChildren();
}

// static
bool AXObjectCacheImpl::IsRelevantPseudoElement(const Node& node) {
  DCHECK(node.IsPseudoElement());
  if (!node.GetLayoutObject())
    return false;

  // ::before, ::after and ::marker are relevant.
  // Allowing these pseudo elements ensures that all visible descendant
  // pseudo content will be reached, despite only being able to walk layout
  // inside of pseudo content.
  // However, AXObjects aren't created for ::first-letter subtrees. The text
  // of ::first-letter is already available in the child text node of the
  // element that the CSS ::first letter applied to.
  if (node.IsMarkerPseudoElement() || node.IsBeforePseudoElement() ||
      node.IsAfterPseudoElement()) {
    // Ignore non-inline whitespace content, which is used by many pages as
    // a "Micro Clearfix Hack" to clear floats without extra HTML tags. See
    // http://nicolasgallagher.com/micro-clearfix-hack/
    if (node.GetLayoutObject()->IsInline())
      return true;  // Inline: not a clearfix hack.
    if (!node.parentNode()->GetLayoutObject() ||
        node.parentNode()->GetLayoutObject()->IsInline()) {
      return true;  // Parent inline: not a clearfix hack.
    }
    const ComputedStyle* style = node.GetLayoutObject()->Style();
    DCHECK(style);
    ContentData* content_data = style->GetContentData();
    if (!content_data)
      return true;
    if (!content_data->IsText())
      return true;  // Not text: not a clearfix hack.
    if (!To<TextContentData>(content_data)
             ->GetText()
             .ContainsOnlyWhitespaceOrEmpty()) {
      return true;  // Not whitespace: not a clearfix hack.
    }
    return false;  // Is the clearfix hack: ignore pseudo element.
  }

  // ::first-letter is relevant if and only if its parent layout object is a
  // relevant pseudo element. If it's not a pseudo element, then this the
  // ::first-letter text would end up being repeated in the AX Tree.
  if (node.IsFirstLetterPseudoElement()) {
    LayoutObject* layout_parent = node.GetLayoutObject()->Parent();
    DCHECK(layout_parent);
    Node* layout_parent_node = layout_parent->GetNode();
    return layout_parent_node && layout_parent_node->IsPseudoElement() &&
           IsRelevantPseudoElement(*layout_parent_node);
  }

  // The remaining possible pseudo element types are not relevant.
  if (node.IsBackdropPseudoElement() || node.IsViewTransitionPseudoElement()) {
    return false;
  }

  // If this is reached, then a new pseudo element type was added and is not
  // yet handled by accessibility. See  PseudoElementTagName() in
  // pseudo_element.cc for all possible types.
  SANITIZER_NOTREACHED() << "Unhandled type of pseudo element on: " << node;
  return false;
}

// static
bool AXObjectCacheImpl::IsRelevantPseudoElementDescendant(
    const LayoutObject& layout_object) {
  if (layout_object.IsText() && To<LayoutText>(layout_object).HasEmptyText())
    return false;
  const LayoutObject* ancestor = &layout_object;
  while (true) {
    ancestor = ancestor->Parent();
    if (!ancestor)
      return false;
    if (ancestor->IsPseudoElement()) {
      // When an ancestor is exposed using CSS alt text, descendants are pruned.
      if (AXNodeObject::GetCSSAltText(ancestor->GetNode()))
        return false;
      return IsRelevantPseudoElement(*ancestor->GetNode());
    }
    if (!ancestor->IsAnonymous())
      return false;
  }
}

AXObject* AXObjectCacheImpl::CreateFromNode(Node* node) {
  if (ShouldCreateAXMenuListOptionFor(node)) {
    return MakeGarbageCollected<AXMenuListOption>(To<HTMLOptionElement>(node),
                                                  *this);
  }

  if (auto* area = DynamicTo<HTMLAreaElement>(node))
    return MakeGarbageCollected<AXImageMapLink>(area, *this);

  return MakeGarbageCollected<AXNodeObject>(node, *this);
}

AXObject* AXObjectCacheImpl::CreateFromInlineTextBox(
    NGAbstractInlineTextBox* inline_text_box) {
  return MakeGarbageCollected<AXInlineTextBox>(inline_text_box, *this);
}

AXObject* AXObjectCacheImpl::GetOrCreate(AccessibleNode* accessible_node,
                                         AXObject* parent) {
  if (AXObject* obj = Get(accessible_node))
    return obj;

  DCHECK_EQ(accessible_node->GetDocument(), &GetDocument());

  DCHECK(parent)
      << "A virtual object must have a parent, and cannot exist without one. "
         "The parent is set when the object is constructed.";

  DCHECK(!accessible_node->element())
      << "The accessible node directly attached to an element should not "
         "have its own AXObject, since the AXObject will be keyed off of the "
         "element instead: "
      << accessible_node->element();

  if (!parent->CanHaveChildren())
    return nullptr;

  AXObject* new_obj =
      MakeGarbageCollected<AXVirtualObject>(*this, accessible_node);
  const AXID ax_id = AssociateAXID(new_obj);
  accessible_node_mapping_.Set(accessible_node, ax_id);
  new_obj->Init(parent);
  return new_obj;
}

AXObject* AXObjectCacheImpl::GetOrCreate(const Node* node) {
  return GetOrCreate(node, nullptr);
}

AXObject* AXObjectCacheImpl::GetOrCreate(Node* node) {
  return GetOrCreate(node, nullptr);
}

AXObject* AXObjectCacheImpl::GetOrCreate(const Node* node,
                                         AXObject* parent_if_known) {
  return GetOrCreate(const_cast<Node*>(node), parent_if_known);
}

AXObject* AXObjectCacheImpl::GetOrCreate(Node* node,
                                         AXObject* parent_if_known) {
  if (!node)
    return nullptr;

  if (AXObject* obj = Get(node)) {
    return obj;
  }

  return CreateAndInit(node, node->GetLayoutObject(), parent_if_known);
}

// Caller must provide a node, a layout object, or both (where they match).
AXObject* AXObjectCacheImpl::CreateAndInit(Node* node,
                                           LayoutObject* layout_object,
                                           AXObject* parent_if_known,
                                           AXID use_axid) {
#if DCHECK_IS_ON()
  DCHECK(node || layout_object);
  DCHECK(!node || !layout_object || layout_object->GetNode() == node);
  DCHECK(!parent_if_known || parent_if_known->CanHaveChildren());
  DCHECK(GetDocument().Lifecycle().GetState() >=
         DocumentLifecycle::kAfterPerformLayout)
      << "Unclean document at lifecycle "
      << GetDocument().Lifecycle().ToString();
  DCHECK(!has_been_disposed_);
#endif  // DCHECK_IS_ON()

  // Determine the type of accessibility object to be created.
  AXObjectType ax_type =
      DetermineAXObjectType(node, layout_object, parent_if_known);
  if (ax_type == kPruneSubtree) {
    return nullptr;
  }

#if DCHECK_IS_ON()
  if (node) {
    DCHECK(layout_object || ax_type != kAXLayoutObject);
    DCHECK(node->isConnected());
    DCHECK(node->GetDocument().GetFrame())
        << "Creating AXObject in a dead document: " << node;
    DCHECK(node->IsElementNode() || node->IsTextNode() ||
           node->IsDocumentNode())
        << "Should only attempt to create AXObjects for the following types of "
           "node types: document, element and text."
        << "\n* Node is: " << node;
  } else {
    // No node, therefore the only possibility is to create an AXLayoutObject.
    DCHECK(layout_object->GetDocument().GetFrame())
        << "Creating AXObject in a dead document: " << layout_object;
    DCHECK_EQ(ax_type, kAXLayoutObject);
    DCHECK(!IsA<LayoutView>(layout_object))
        << "AXObject for document is always created with a node.";
  }
#endif

  // Determine the parent.
  AXObject* parent = nullptr;
  if (parent_if_known) {
    // Parent is known because the tree is being explored downward, and as the
    // parent adds its children it passes itself in.
    parent = parent_if_known;
  } else if (node == &GetDocument()) {
    // The root object does not have a parent.
    parent = nullptr;
  } else {
    // Must compute the parent, which occurs when an AXObject is being created
    // in the middle of the tree.
    parent = AXObject::ComputeNonARIAParent(*this, node);

    // Only rebuild the child list of the parent if we had to compute
    // the parent here, and it wasn't passed in as context. In other situations,
    // we should know about the child already.
    if (parent) {
      DCHECK(!parent->IsDetached());
      parent->ChildrenChangedWithCleanLayout();
    }
    // The parent can become detached in ChildrenChangedWithCleanLayout.
    if (!parent || parent->IsDetached()) {
      // An AXObject must have a parent, unless it's the root.
      // This because when no parent can be computed, it means that any AXObject
      // we would create would not have a path to the root. We do not create
      // ophaned AXObjects, so return null.
      return nullptr;
    }
  }

  DCHECK(!IsFrozen()) << "Can't create AXObject while tree is frozen: " << node;

  AXID axid = GenerateAXID();
  DCHECK(!base::Contains(objects_, axid));

  if (node) {
    DCHECK(!node_object_mapping_.Contains(node))
        << "Already have an AXObject for " << node;
    node_object_mapping_.Set(node, axid);
  } else {
    DCHECK(!layout_object_mapping_.Contains(layout_object))
        << "Already have an AXObject for " << layout_object;
    layout_object_mapping_.Set(layout_object, axid);
  }

  // Create the new AXObject.
  AXObject* new_obj = nullptr;
  if (ax_type == kAXLayoutObject) {
    // Prefer to create from renderer if there is a layout object because
    // AXLayoutObjects can provide information about bounding boxes.
    new_obj = CreateFromRenderer(layout_object);
  } else {
    new_obj = CreateFromNode(node);
  }
  DCHECK(new_obj) << "Could not create AXObject.";

  // Give the AXObject its ID and initialize.
  AssociateAXID(new_obj, axid);
  new_obj->Init(parent);

  // Register incomplete relations with the relation cache, so that when the
  // target id shows up at a later time, the source node can be reserialized
  // with the completed relation.
  relation_cache_->RegisterIncompleteRelations(new_obj);

  return new_obj;
}

AXObject* AXObjectCacheImpl::GetOrCreate(LayoutObject* layout_object) {
  return GetOrCreate(layout_object, nullptr);
}

AXObject* AXObjectCacheImpl::GetOrCreate(LayoutObject* layout_object,
                                         AXObject* parent_if_known) {
  if (!layout_object)
    return nullptr;

  if (AXObject* obj = Get(layout_object, parent_if_known)) {
    return obj;
  }

  return CreateAndInit(layout_object->GetNode(), layout_object,
                       parent_if_known);
}

AXObject* AXObjectCacheImpl::GetOrCreate(
    NGAbstractInlineTextBox* inline_text_box,
    AXObject* parent) {
  if (!inline_text_box)
    return nullptr;

  if (!parent) {
    LayoutText* layout_text_parent = inline_text_box->GetLayoutText();
    DCHECK(layout_text_parent);
    parent = GetOrCreate(layout_text_parent);
    if (!parent) {
      DCHECK(inline_text_box->GetText().ContainsOnlyWhitespaceOrEmpty() ||
             !IsRelevantPseudoElementDescendant(*layout_text_parent))
          << "No parent for non-whitespace inline textbox: "
          << layout_text_parent
          << "\nParent of parent: " << layout_text_parent->Parent();
      return nullptr;
    }
  }

  // Inline textboxes are included if and only if the parent is unignored.
  // If the parent is ignored but included in tree, the inline textbox is
  // still withheld.
  if (parent->LastKnownIsIgnoredValue()) {
    return nullptr;
  }

  if (AXObject* obj = Get(inline_text_box)) {
#if DCHECK_IS_ON()
    DCHECK(!obj->IsDetached())
        << "AXObject for inline text box should not be detached: "
        << obj->ToString(true, true);
    // AXInlineTextbox objects can't get a new parent, unlike other types of
    // accessible objects that can get a new parent because they moved or
    // because of aria-owns.
    // AXInlineTextbox objects are only added via AddChildren() on static text
    // or line break parents. The children are cleared, and detached from their
    // parent before AddChildren() executes. There should be no previous parent.
    DCHECK(parent->RoleValue() == ax::mojom::blink::Role::kStaticText ||
           parent->RoleValue() == ax::mojom::blink::Role::kLineBreak);
    DCHECK(!obj->CachedParentObject() || obj->CachedParentObject() == parent)
        << "Mismatched old and new parent:"
        << "\n* Old parent: " << obj->CachedParentObject()->ToString(true, true)
        << "\n* New parent: " << parent->ToString(true, true);
    DCHECK(ui::CanHaveInlineTextBoxChildren(parent->RoleValue()))
        << "Unexpected parent of inline text box: " << parent->RoleValue();
#endif
    DCHECK(obj->ParentObject() == parent);
    return obj;
  }

  AXObject* new_obj = CreateFromInlineTextBox(inline_text_box);

  const AXID axid = AssociateAXID(new_obj);

  inline_text_box_object_mapping_.Set(inline_text_box, axid);
  new_obj->Init(parent);
  return new_obj;
}

AXObject* AXObjectCacheImpl::CreateAndInit(ax::mojom::blink::Role role,
                                           AXObject* parent) {
  DCHECK(parent);
  DCHECK(parent->CanHaveChildren());
  AXObject* obj = nullptr;

  switch (role) {
    case ax::mojom::blink::Role::kMenuListPopup:
      DCHECK(use_ax_menu_list_);
      obj = MakeGarbageCollected<AXMenuListPopup>(*this);
      break;
    default:
      obj = nullptr;
  }

  if (!obj)
    return nullptr;

  AssociateAXID(obj);

  obj->Init(parent);
  return obj;
}

void AXObjectCacheImpl::Remove(AXObject* object, bool notify_parent) {
  DCHECK(object);
  if (object->IsAXInlineTextBox()) {
    Remove(object->GetInlineTextBox(), notify_parent);
  } else if (object->GetNode()) {
    Remove(object->GetNode(), notify_parent);
  } else if (object->GetLayoutObject()) {
    Remove(object->GetLayoutObject(), notify_parent);
  } else if (object->GetAccessibleNode()) {
    Remove(object->GetAccessibleNode(), notify_parent);
  } else {
    Remove(object->AXObjectID(), notify_parent);
  }
}

// This is safe to call even if there isn't a current mapping.
// This is called by other Remove() methods, called by Blink for DOM and layout
// changes, iterating over all removed content in the subtree:
// - When a DOM subtree is removed, it is called with the root node first, and
//   then descending down into the subtree.
// - When layout for a subtree is detached, it is called on layout objects,
//   starting with leaves and moving upward, ending with the subtree root.
void AXObjectCacheImpl::Remove(AXID ax_id, bool notify_parent) {
  DCHECK(!IsFrozen());

  if (!ax_id)
    return;

  // First, fetch object to operate some cleanup functions on it.
  auto it = objects_.find(ax_id);
  AXObject* obj = it != objects_.end() ? it->value : nullptr;
  if (!obj)
    return;

  if (notify_parent && !has_been_disposed_) {
    ChildrenChangedOnAncestorOf(obj);
  }

  obj->Detach();

  RemoveReferencesToAXID(ax_id);

  // Remove the object.
  // TODO(accessibility) We don't use the return value, can we use .erase()
  // and it will still make sure that the object is cleaned up?
  objects_.Take(ax_id);

  // Removing an aria-modal dialog can affect the entire tree.
  if (active_aria_modal_dialog_ == obj) {
    Settings* settings = GetSettings();
    if (settings && settings->GetAriaModalPrunesAXTree()) {
      MarkDocumentDirty();
    }
    active_aria_modal_dialog_ = nullptr;
  }
}

// This is safe to call even if there isn't a current mapping.
void AXObjectCacheImpl::Remove(AccessibleNode* accessible_node) {
  Remove(accessible_node, /* notify_parent */ true);
}

void AXObjectCacheImpl::Remove(AccessibleNode* accessible_node,
                               bool notify_parent) {
  DCHECK(accessible_node);

  auto iter = accessible_node_mapping_.find(accessible_node);
  if (iter == accessible_node_mapping_.end())
    return;

  AXID ax_id = iter->value;
  accessible_node_mapping_.erase(iter);

  Remove(ax_id, notify_parent);
}

// This is safe to call even if there isn't a current mapping.
void AXObjectCacheImpl::Remove(LayoutObject* layout_object) {
  Remove(layout_object, /* notify_parent */ true);
}

void AXObjectCacheImpl::Remove(LayoutObject* layout_object,
                               bool notify_parent) {
  if (!layout_object)
    return;

  if (IsA<LayoutView>(layout_object)) {
    // A document is being destroyed.
    // This code is only reached when it is a popup being destroyed.
    // TODO(accessibility) Can we remove this case since Blink calls
    // RemovePopup(document) for us?
    DCHECK(!popup_document_ ||
           popup_document_ == &layout_object->GetDocument());
    // Popup has been destroyed.
    if (popup_document_) {
      RemovePopup(popup_document_);
    }
  }

  // If a DOM node is present, it will have been used to back the AXObject, in
  // which case we need to call Remove(node) instead.
  if (Node* node = layout_object->GetNode()) {
    // Pseudo elements are a special case. They need to be marked dirty so that
    // their entire subtree is recomputed (it is disappearing or changing).
    if (node->IsPseudoElement()) {
      DeferTreeUpdate(TreeUpdateReason::kMarkDirtyFromRemove, node);
    }
    // Shadow root subtrees that don't have layout objects for the assigned
    // nodes will not reach Node::RemovedFromFlatTree() and therefore the
    // safest thing to do is ensure everything under a shadow host is removed
    // when the host itself is removed.
    if (node->GetShadowRoot()) {
      RemoveSubtreeWhenSafe(node);
    }
    if (layout_object->Style() &&
        !layout_object->Style()->IsContentVisibilityVisible()) {
      // If a content-visibility: auto/hidden node is removed, remove the entire
      // subtree because any AXObject descendants are now invalid, and there
      // will not be any other signals to hook for invalidation or removal.
      RemoveSubtreeWhenSafe(node);
    }
    if (IsA<HTMLImageElement>(node)) {
      // If an image is removed, ensure its entire subtree is deleted as there
      // may have been children supplied via a map.
      if (auto* layout_image = DynamicTo<LayoutImage>(layout_object)) {
        if (auto* map = layout_image->ImageMap()) {
          if (map->ImageElement() == node) {
            RemoveSubtreeWhenSafe(map, false);
          }
        }
      }
    }

    Remove(node, notify_parent);
    return;
  }

  auto iter = layout_object_mapping_.find(layout_object);
  if (iter == layout_object_mapping_.end())
    return;

  AXID ax_id = iter->value;
  DCHECK(ax_id);

  layout_object_mapping_.erase(iter);
  Remove(ax_id, notify_parent);
}

// This is safe to call even if there isn't a current mapping.
void AXObjectCacheImpl::Remove(Node* node) {
  Remove(node, /* notify_parent */ true);
}

void AXObjectCacheImpl::Remove(Node* node, bool notify_parent) {
  if (!node)
    return;

  auto iter = node_object_mapping_.find(node);
  if (iter != node_object_mapping_.end()) {
    LayoutObject* layout_object = node->GetLayoutObject();
    DCHECK(!layout_object || layout_object_mapping_.find(layout_object) ==
                                 layout_object_mapping_.end())
        << "AXObject cannot be backed by both a layout object and node.";
    AXID ax_id = iter->value;
    DCHECK(ax_id);
    node_object_mapping_.erase(iter);
    Remove(ax_id, notify_parent);
  }
}

void AXObjectCacheImpl::RemovePopup(Document* popup_document) {
  // The only 2 documents that partake in the cache are the main document and
  // the popup document. This method is only be called for the popup document,
  // because if the main document is shutting down, the cache is disposed.
  DCHECK(popup_document);
  DCHECK(IsPopup(*popup_document)) << "Use Dispose() to remove main document.";
  RemoveSubtreeWhenSafe(popup_document);

  popup_document_ = nullptr;
  notifications_to_post_popup_.clear();
  tree_update_callback_queue_popup_.clear();
  invalidated_ids_popup_.clear();
}

// This is safe to call even if there isn't a current mapping.
void AXObjectCacheImpl::Remove(NGAbstractInlineTextBox* inline_text_box) {
  Remove(inline_text_box, /* notify_parent */ true);
}

void AXObjectCacheImpl::Remove(NGAbstractInlineTextBox* inline_text_box,
                               bool notify_parent) {
  if (!inline_text_box)
    return;

  auto iter = inline_text_box_object_mapping_.find(inline_text_box);
  if (iter == inline_text_box_object_mapping_.end())
    return;

  AXID ax_id = iter->value;
  inline_text_box_object_mapping_.erase(iter);

  Remove(ax_id, notify_parent);
}

void AXObjectCacheImpl::RemoveIncludedSubtree(AXObject* object,
                                              bool remove_root) {
  DCHECK(object);
  if (object->IsDetached()) {
    return;
  }

  for (const auto& ax_child : object->CachedChildrenIncludingIgnored()) {
    RemoveIncludedSubtree(ax_child, /* remove_root */ true);
  }
  if (remove_root) {
    Remove(object, /* notify_parent */ false);
  }
}

void AXObjectCacheImpl::ProcessSubtreeRemovals() {
  for (auto& node : nodes_for_subtree_removal_) {
    ProcessSubtreeRemoval(node.first, node.second);
  }
  nodes_for_subtree_removal_.clear();
}

void AXObjectCacheImpl::ProcessSubtreeRemoval(Node* node, bool remove_root) {
  if (remove_root) {
    RemoveSubtreeWithFlatTraversal(node, /* remove root */ true,
                                   /* notify_parent */ true);
  } else {
    for (Node* child_node = LayoutTreeBuilderTraversal::FirstChild(*node);
         child_node;
         child_node = LayoutTreeBuilderTraversal::NextSibling(*child_node)) {
      RemoveSubtreeWithFlatTraversal(child_node, /* remove root */ true,
                                     /* notify_parent */ true);
    }
  }
}

void AXObjectCacheImpl::RemoveSubtreeWhenSafe(Node* node) {
  RemoveSubtreeWhenSafe(node, true);
}

void AXObjectCacheImpl::RemoveSubtreeWhenSafe(Node* node, bool remove_root) {
  if (!node || !node->isConnected()) {
    return;
  }
  if (AXObject::CanSafelyUseFlatTreeTraversalNow(node->GetDocument())) {
    ProcessSubtreeRemoval(node, remove_root);
    return;
  }
  nodes_for_subtree_removal_.push_back(std::make_pair(node, remove_root));
}

void AXObjectCacheImpl::RemoveSubtreeWithFlatTraversal(const Node* node,
                                                       bool remove_root,
                                                       bool notify_parent) {
  DCHECK(node);
  // Previously used DCHECK(AXObject::CanSafelyUseFlatTreeTraversalNow()) but
  // failed because document had pending slot assignment in
  // external/wpt/dom/nodes/node-appendchild-crash.html.
  DCHECK(!node->GetDocument().IsFlatTreeTraversalForbidden());
  AXObject* object = SafeGet(node);
  if (!object && !remove_root) {
    // Nothing remaining to do for this subtree. Already removed.
    return;
  }

  if (!IsA<ShadowRoot>(node)) {
    // Remove children found through flat traversal.
    for (Node* child_node = LayoutTreeBuilderTraversal::FirstChild(*node);
         child_node;
         child_node = LayoutTreeBuilderTraversal::NextSibling(*child_node)) {
      RemoveSubtreeWithFlatTraversal(child_node, /* remove_root */ true,
                                     /* notify_parent */ false);
    }
  }

  if (!object) {
    return;
  }

  // When removing children, use the cached children to avoid creating a child
  // just to destroy it.
  for (AXObject* ax_included_child : object->CachedChildrenIncludingIgnored()) {
    if (ax_included_child->CachedParentObject() != object) {
      continue;
    }
    if (ui::CanHaveInlineTextBoxChildren(object->RoleValue())) {
      // Just remove child inline textboxes, don't use their node which is the
      // same as that static text's parent and would cause an infinite loop.
      Remove(ax_included_child, /* notify_parent */ false);
    } else if (ax_included_child->GetNode()) {
      DCHECK(ax_included_child->GetNode() != node);
      RemoveSubtreeWithFlatTraversal(ax_included_child->GetNode(),
                                     /* remove_root */ true,
                                     /* notify_parent */ false);
    } else {
      RemoveIncludedSubtree(ax_included_child, /* remove_root */ true);
    }
  }

  // The code below uses ChildrenChangedWithCleanLayout() instead of
  // notify_parent param in Remove(), which would be queued, and it needs to
  // happen immediately.
  AXObject* parent_to_notify =
      notify_parent ? object->CachedParentObject() : nullptr;
  if (remove_root) {
    Remove(object, /* notify_parent */ false);
  }
  if (parent_to_notify) {
    if (processing_deferred_events_) {
      ChildrenChangedWithCleanLayout(parent_to_notify);
    } else {
      ChildrenChanged(parent_to_notify);
    }
  }
}

void AXObjectCacheImpl::InvalidateCachedValuesOnSubtreeWithCleanLayout(
    Node* node) {
  if (AXObject* object = GetOrCreate(node)) {
    ax_tree_serializer_->MarkSubtreeDirty(object);

    // Store the parent for later children changed notification in case object
    // is detached from parent during processing.
    AXObject* parent_to_notify = object->ParentObject();

    DCHECK(AXObject::CanSafelyUseFlatTreeTraversalNow(*object->GetDocument()))
        << "Cannot remove children now: " << object->ToString(true, true);

    InvalidateCachedValuesOnSubtreeWithCleanLayoutRecursive(object);

    // Notify the subtree's parent if necessary.
    ChildrenChangedWithCleanLayout(parent_to_notify);
  }
}

void AXObjectCacheImpl::InvalidateCachedValuesOnSubtreeWithCleanLayoutRecursive(
    AXObject* object) {
  DCHECK(object);
  if (object->IsDetached()) {
    return;
  }

  // Invalidate the parent before its children, because some child cached values
  // are dependent on the parent values.
  bool was_included = object->LastKnownIsIncludedInTreeValue();
  object->InvalidateCachedValues();
  object->UpdateCachedAttributeValuesIfNeeded(/* notify_parent */ false);
  bool is_included = object->AccessibilityIsIncludedInTree();
  // If the included state changes, the parents all the way up to the first
  // included ancestor must update their children. A children changed event does
  // not need to be fired for every node here -- it's enough to fire for the
  // ancestor of the whole subtree, which is done in the non-recursive caller.
  if (was_included != is_included) {
    if (AXObject* parent = object->ParentObject()) {
      if (AXObject* included_parent = InvalidateChildren(parent)) {
        included_parent->SetNeedsToUpdateChildren();
      }
    }
  }

  // Set of all children, whether in included or not.
  HeapHashSet<Member<AXObject>> children;

  // Gather the updated included children list. In some cases, the children are
  // dirty and need to be refreshed. Any objects reused for the child refresh
  // will first update their cached values, in order to make sure they are
  // included and actually should be added.
  if (was_included || is_included) {
    for (AXObject* ax_included_child : object->ChildrenIncludingIgnored()) {
      children.insert(ax_included_child);
    }
  }

  // Gather children found through flat traversal that were not included.
  Node* node = object->GetNode();
  if (node) {
    for (Node* child_node = LayoutTreeBuilderTraversal::FirstChild(*node);
         child_node;
         child_node = LayoutTreeBuilderTraversal::NextSibling(*child_node)) {
      if (AXObject* ax_unincluded_child = GetOrCreate(child_node)) {
        children.insert(ax_unincluded_child);
      }
    }
  }

  // Recurse through the de-duped list of children.
  for (AXObject* child : children) {
    InvalidateCachedValuesOnSubtreeWithCleanLayoutRecursive(child);
  }
}

AXID AXObjectCacheImpl::GenerateAXID() const {
  static AXID last_used_id = 0;

  // Generate a new ID.
  AXID obj_id = last_used_id;
  do {
    ++obj_id;
  } while (!obj_id || WTF::IsHashTraitsDeletedValue<HashTraits<AXID>>(obj_id) ||
           objects_.Contains(obj_id));

  last_used_id = obj_id;

  return obj_id;
}

void AXObjectCacheImpl::AddAriaNotification(
    Node* node,
    const String announcement,
    const AriaNotificationOptions* options) {
  aria_notifications_.push_back(
      MakeGarbageCollected<AriaNotification>(node, announcement, options));
}

void AXObjectCacheImpl::AddToFixedOrStickyNodeList(const AXObject* object) {
  DCHECK(object);
  DCHECK(!object->IsDetached());
  fixed_or_sticky_node_ids_.insert(object->AXObjectID());
}

AXID AXObjectCacheImpl::AssociateAXID(AXObject* obj, AXID use_axid) {
  // Check for already-assigned ID.
  DCHECK(!obj->AXObjectID()) << "Object should not already have an AXID";

  const AXID new_axid = use_axid ? use_axid : GenerateAXID();

  obj->SetAXObjectID(new_axid);
  objects_.Set(new_axid, obj);

  return new_axid;
}

void AXObjectCacheImpl::RemoveReferencesToAXID(AXID obj_id) {
  DCHECK(!WTF::IsHashTraitsDeletedValue<HashTraits<AXID>>(obj_id));

  // Clear AXIDs from maps. Note: do not need to erase id from
  // changed_bounds_ids_, a set which is cleared each time
  // SerializeLocationChanges() is finished. Also, do not need to erase id from
  // invalidated_ids_main_ or invalidated_ids_popup_, which are cleared each
  // time ProcessInvalidatedObjects() finishes, and having extra ids in those
  // sets is not harmful.
  autofill_state_map_.erase(obj_id);
  fixed_or_sticky_node_ids_.erase(obj_id);
  cached_bounding_boxes_.erase(obj_id);
  // Clear id from relation cache.
  relation_cache_->RemoveAXID(obj_id);
}

AXObject* AXObjectCacheImpl::NearestExistingAncestor(Node* node) {
  // Find the nearest ancestor that already has an accessibility object, since
  // we might be in the middle of a layout.
  while (node) {
    if (AXObject* obj = Get(node))
      return obj;
    node = node->parentNode();
  }
  return nullptr;
}

void AXObjectCacheImpl::UpdateNumTreeUpdatesQueuedBeforeLayoutHistogram() {
  UMA_HISTOGRAM_COUNTS_100000(
      "Blink.Accessibility.NumTreeUpdatesQueuedBeforeLayout",
      tree_update_callback_queue_main_.size() +
          tree_update_callback_queue_popup_.size());
}

void AXObjectCacheImpl::InvalidateBoundingBoxForFixedOrStickyPosition() {
  for (AXID id : fixed_or_sticky_node_ids_)
    changed_bounds_ids_.insert(id);
}

bool AXObjectCacheImpl::CanDeferTreeUpdate(Document* tree_update_document) {
  DCHECK(!has_been_disposed_);
  DCHECK(!IsFrozen());

  if (!IsActive(GetDocument()) || tree_updates_paused_)
    return false;

  // Ensure the tree update document is in a good state.
  if (!tree_update_document || !IsActive(*tree_update_document)) {
    return false;
  }

  return true;
}

bool AXObjectCacheImpl::PauseTreeUpdatesIfQueueFull() {
  // Check the main document's queue. If there are too many entries, pause all
  // updates and resume later after rebuilding the tree from scratch.
  // Popup is excluded because it's controlled by us and will not have too many
  // updates. In the case of a web page having too many updates, we need to
  // clear all queues, including the popup's.
  if (tree_update_callback_queue_main_.size() >= max_pending_updates_) {
    UpdateNumTreeUpdatesQueuedBeforeLayoutHistogram();
    tree_updates_paused_ = true;
    LOG(INFO) << "Accessibility tree update queue is too big, updates have "
                 "been paused";
    // Clear updates from both documents.
    tree_update_callback_queue_main_.clear();
    tree_update_callback_queue_popup_.clear();
    return true;
  }

  return false;
}

void AXObjectCacheImpl::DeferTreeUpdate(
    AXObjectCacheImpl::TreeUpdateReason update_reason,
    Node* node,
    ax::mojom::blink::Event event) {
  DCHECK(node);
  DCHECK(!has_been_disposed_);
  DCHECK(!IsFrozen());

  Document& tree_update_document = node->GetDocument();
  if (!CanDeferTreeUpdate(&tree_update_document)) {
    return;
  }

  if (PauseTreeUpdatesIfQueueFull()) {
    return;
  }

  TreeUpdateCallbackQueue& queue =
      GetTreeUpdateCallbackQueue(tree_update_document);

  queue.push_back(MakeGarbageCollected<TreeUpdateParams>(
      node, 0u, ComputeEventFrom(), active_event_from_action_,
      ActiveEventIntents(), update_reason, event));

  if (AXObject* obj = SafeGet(node)) {
    obj->InvalidateCachedValues();
  }

  // These events are fired during RunPostLifecycleTasks(),
  // ensure there is a document lifecycle update scheduled.
  ScheduleAXUpdate();
}
void AXObjectCacheImpl::DeferTreeUpdate(
    AXObjectCacheImpl::TreeUpdateReason update_reason,
    AXObject* obj,
    ax::mojom::blink::Event event) {
  // Called for updates that do not have a DOM node, e.g. a children or text
  // changed event that occurs on an anonymous layout block flow.
  DCHECK(obj);

  if (obj->IsDetached()) {
    return;
  }

  DCHECK(obj->AXObjectID());

  Document* tree_update_document = obj->GetDocument();

  if (!CanDeferTreeUpdate(tree_update_document)) {
    return;
  }

  if (PauseTreeUpdatesIfQueueFull()) {
    return;
  }

  TreeUpdateCallbackQueue& queue =
      GetTreeUpdateCallbackQueue(*tree_update_document);

  queue.push_back(MakeGarbageCollected<TreeUpdateParams>(
      nullptr, obj->AXObjectID(), ComputeEventFrom(), active_event_from_action_,
      ActiveEventIntents(), update_reason, event));

  obj->InvalidateCachedValues();

  // These events are fired during RunPostLifecycleTasks(),
  // ensure there is a document lifecycle update scheduled.
  ScheduleAXUpdate();
}

void AXObjectCacheImpl::SelectionChanged(Node* node) {
  if (!node)
    return;

  Settings* settings = GetSettings();
  if (settings && settings->GetAriaModalPrunesAXTree())
    UpdateActiveAriaModalDialog(node);

  // Firing the document selection changed event triggers the immediate
  // serialization that is desired for user input events -- see
  // IsImmediateProcessingRequiredForEvent().
  PostNotification(&GetDocument(),
                   ax::mojom::blink::Event::kDocumentSelectionChanged);

  // If there is a text control, mark it dirty to serialize
  // IntAttribute::kTextSelStart/kTextSelEnd changes.
  // TODO(accessibility) Remove once we remove kTextSelStart/kTextSelEnd.
  if (TextControlElement* text_control = EnclosingTextControl(node))
    MarkElementDirty(text_control);
}

void AXObjectCacheImpl::UpdateReverseTextRelations(
    const AXObject* relation_source,
    const Vector<String>& target_ids) {
  relation_cache_->UpdateReverseTextRelations(relation_source->GetNode(),
                                              target_ids);
}

void AXObjectCacheImpl::StyleChanged(const LayoutObject* layout_object,
                                     bool visibility_or_inertness_changed) {
  DCHECK(layout_object);
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();
  AXObject* ax_object = SafeGet(layout_object->GetNode());
  if (!ax_object) {
    // No object exists to mark dirty yet -- there can sometimes be a layout in
    // the initial empty document, or style has changed before the object cache
    // becomes aware that the node exists. It's too early for the style change
    // to be useful.
    return;
  }

  if (visibility_or_inertness_changed) {
    ChildrenChanged(ax_object);
  }
  MarkAXObjectDirty(ax_object);
}

void AXObjectCacheImpl::TextOffsetsChanged(const LayoutBlockFlow* block_flow) {
  if (AXObject* obj = Get(block_flow)) {
    DeferTreeUpdate(TreeUpdateReason::kTextOffsetsChanged, obj);
  }
}

void AXObjectCacheImpl::TextOffsetsChangedWithCleanLayout(AXObject* obj) {
  if (!obj || obj->IsDetached()) {
    return;
  }
#if DCHECK_IS_ON()
  Document* document = obj->GetDocument();
  DCHECK(document->Lifecycle().GetState() >= DocumentLifecycle::kLayoutClean)
      << "Unclean document at lifecycle " << document->Lifecycle().ToString();
#endif  // DCHECK_IS_ON()

  // Text changing for a block flow invalidates all of the
  // text strings for children, such as via LayoutObject::GetName().
  if (obj->AccessibilityIsIncludedInTree()) {
    MarkAXSubtreeDirtyWithCleanLayout(obj);
  }
}

void AXObjectCacheImpl::TextChanged(Node* node) {
  if (!node)
    return;

  // A text changed event is redundant with children changed on the same node.
  if (base::Contains(nodes_with_pending_children_changed_, node)) {
    return;
  }

  DeferTreeUpdate(TreeUpdateReason::kTextChangedFromTextChangedNode, node);
}

void AXObjectCacheImpl::TextChanged(const LayoutObject* layout_object) {
  if (!layout_object)
    return;

  // The node may be null when the text changes on an anonymous layout object,
  // such as a layout block flow that is inserted to parent an inline object
  // when it has a block sibling.
  Node* node = GetClosestNodeForLayoutObject(layout_object);
  if (node) {
    // A text changed event is redundant with children changed on the same node.
    if (base::Contains(nodes_with_pending_children_changed_, node)) {
      return;
    }

    DeferTreeUpdate(TreeUpdateReason::kTextChangedFromTextChangedNode, node);
    return;
  }

  if (Get(layout_object)) {
    DeferTreeUpdate(TreeUpdateReason::kTextChangedFromTextChangedAXObject,
                    Get(layout_object));
  }
}

void AXObjectCacheImpl::TextChangedWithCleanLayout(
    Node* optional_node_for_relation_update,
    AXObject* obj) {
  if (obj ? obj->IsDetached() : !optional_node_for_relation_update)
    return;

#if DCHECK_IS_ON()
  Document* document = obj ? obj->GetDocument()
                           : &optional_node_for_relation_update->GetDocument();
  DCHECK(document->Lifecycle().GetState() >= DocumentLifecycle::kLayoutClean)
      << "Unclean document at lifecycle " << document->Lifecycle().ToString();
#endif  // DCHECK_IS_ON()

  if (obj) {
    if (obj->RoleValue() == ax::mojom::blink::Role::kStaticText &&
        obj->AccessibilityIsIncludedInTree()) {
      if (InlineTextBoxAccessibilityEnabled()) {
        // Update inline text box children.
        ChildrenChangedWithCleanLayout(optional_node_for_relation_update, obj);
        return;
      }
    }

    MarkAXObjectDirtyWithCleanLayout(obj);
  }

  if (optional_node_for_relation_update)
    relation_cache_->UpdateRelatedTree(optional_node_for_relation_update, obj);
}

void AXObjectCacheImpl::TextChangedWithCleanLayout(Node* node) {
  if (!node)
    return;

  DCHECK(!node->GetDocument().NeedsLayoutTreeUpdateForNode(*node));
  TextChangedWithCleanLayout(node, GetOrCreate(node));
}

void AXObjectCacheImpl::FocusableChangedWithCleanLayout(Node* node) {
  Element* element = To<Element>(node);
  DCHECK(!element->GetDocument().NeedsLayoutTreeUpdateForNode(*element));
  AXObject* obj = GetOrCreate(element);
  if (!obj)
    return;

  if (obj->IsAriaHidden()) {
    // Elements that are hidden but focusable are not ignored. Therefore, if a
    // hidden element's focusable state changes, it's ignored state must be
    // recomputed. It may be newly included in the tree, which means the
    // parents must be updated.
    // TODO(accessibility) Is this necessary? We have other places in the code
    // that automatically do a children changed on parents of nodes whose
    // ignored or included states change.
    ChildrenChangedWithCleanLayout(obj->CachedParentObject());
  }

  // Refresh the focusable state and State::kIgnored on the exposed object.
  MarkAXObjectDirtyWithCleanLayout(obj);
}

void AXObjectCacheImpl::DocumentTitleChanged() {
  DocumentLifecycle::DisallowTransitionScope disallow(document_->Lifecycle());

  AXObject* root = Get(document_);
  if (root)
    PostNotification(root, ax::mojom::blink::Event::kDocumentTitleChanged);
}

void AXObjectCacheImpl::UpdateCacheAfterNodeIsAttached(Node* node) {
  DCHECK(node);
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  // It's not necessary to process text nodes here,because we'll also get a call
  // for the attachment of the parent element.
  if (IsA<Text>(node)) {
    return;
  }

  Document* document = DynamicTo<Document>(node);
  if (document) {
    // A popup is being shown.
    DCHECK(*document != GetDocument());
    DCHECK(!popup_document_) << "Last popup was not cleared.";
    DCHECK(!popup_document_ || popup_document_ == document)
        << "Last popup was not cleared: " << (void*)popup_document_;
    popup_document_ = document;
    DCHECK(IsPopup(*document));
    // Fire children changed on the focused element that owns this popup.
    ChildrenChanged(GetDocument().FocusedElement());
    return;
  }

  // If the node is the root of a display locked subtree, and it already had an
  // AXObject, its entire subtree needs to be invalidated. Now that it has
  // layout, its subtree will be rebuilt using AXLayoutObject rather than
  // AXNodeObject.
  if (node->GetLayoutObject() && node->GetLayoutObject()->Style() &&
      !node->GetLayoutObject()->Style()->IsContentVisibilityVisible() &&
      node_object_mapping_.Contains(node)) {
    RemoveSubtreeWithFlatTraversal(node, /* remove_root */ false,
                                   /* notify_parent */ false);
  }

  DeferTreeUpdate(TreeUpdateReason::kUpdateCacheAfterNodeIsAttached, node);
}

void AXObjectCacheImpl::UpdateCacheAfterNodeIsAttachedWithCleanLayout(
    Node* node) {
  if (!node || !node->isConnected()) {
    return;
  }

  Element* element = DynamicTo<Element>(node);

#if DCHECK_IS_ON()
  DCHECK(node->GetDocument().Lifecycle().GetState() >=
         DocumentLifecycle::kLayoutClean)
      << "Unclean document at lifecycle "
      << node->GetDocument().Lifecycle().ToString();
#endif  // DCHECK_IS_ON()

  // Process any relation attributes that can affect ax objects already created.

  // Force computation of aria-owns, so that original parents that already
  // computed their children get the aria-owned children removed.
  if (AXObject::HasARIAOwns(element)) {
    if (AXObject* obj = GetOrCreate(element)) {
      relation_cache_->UpdateAriaOwnsWithCleanLayout(obj);
    }
  }

  if (AccessibleNode::GetPropertyOrARIAAttributeValue(
          element, AOMRelationProperty::kActiveDescendant)) {
    HandleActiveDescendantChangedWithCleanLayout(element);
  }

  AXObject* obj = Get(node);
  MaybeNewRelationTarget(*node, obj);

  // Even if the node or parent are ignored, an ancestor may need to include
  // descendants of the attached node, thus ChildrenChangedWithCleanLayout()
  // must be called. It handles ignored logic, ensuring that the first ancestor
  // that should have this as a child will be updated.
  Node* parent_node = IsA<ShadowRoot>(node)
                          ? &To<ShadowRoot>(node)->host()
                          : LayoutTreeBuilderTraversal::Parent(*node);
  ChildrenChangedWithCleanLayout(parent_node);

  // If an image map area is added, we need to update children on the image.
  if (IsA<HTMLAreaElement>(node))
    ChildrenChangedWithCleanLayout(AXObject::ComputeNonARIAParent(*this, node));

  // Rare edge case: if an image is added, it could have changed the order of
  // images with the same usemap in the document. Only the first image for a
  // given <map> should have the <area> children. Therefore, get the current
  // primary image before it's updated, and ensure its children are
  // recalculated.
  if (IsA<HTMLImageElement>(node)) {
    if (HTMLMapElement* map = AXObject::GetMapForImage(node)) {
      HTMLImageElement* primary_image_element = map->ImageElement();
      if (node != primary_image_element) {
        ChildrenChangedWithCleanLayout(SafeGet(primary_image_element));
      } else if (AXObject* ax_previous_parent = GetAXImageForMap(*map)) {
        if (ax_previous_parent != obj) {
          ChildrenChangedWithCleanLayout(ax_previous_parent->GetNode(),
                                         ax_previous_parent);
          ax_previous_parent->ClearChildren();
        }
      }
    }
  }

  // Check if a row or cell's table changed to or from a data table.
  if (IsA<HTMLTableRowElement>(node) || IsA<HTMLTableCellElement>(node)) {
    Element* parent = node->parentElement();
    while (parent) {
      if (DynamicTo<HTMLTableElement>(parent)) {
        break;
      }
      parent = parent->parentElement();
    }
    if (parent) {
      UpdateTableRoleWithCleanLayout(parent);
    }
    TableCellRoleMaybeChanged(node);
  }
}

void AXObjectCacheImpl::DidInsertChildrenOfNode(Node* node) {
  // If a node is inserted, notify its parent that its text/children may have
  // changed.
  DCHECK(node);
  while (node) {
    if (SafeGet(node, true)) {
      TextChanged(node);
      return;
    }
    node = NodeTraversal::Parent(*node);
  }
}

// Note: do not call this when a child is becoming newly included, because
// it will return early if |obj| was last known to be unincluded.
void AXObjectCacheImpl::ChildrenChangedOnAncestorOf(AXObject* obj) {
  DCHECK(obj);
  DCHECK(!obj->IsDetached());

  // If |obj| is not included, and it has no included descendants, then there is
  // nothing in any ancestor's cached children that needs clearing. This rule
  // improves performance when removing an entire subtree of unincluded nodes.
  // For example, if a <div id="root" style="display:none"> will be
  // included because it is a potential relation target. If unincluded
  // descendants change, no ChildrenChanged() processing is necessary, because
  // #root has no children.
  if (!obj->LastKnownIsIncludedInTreeValue() &&
      obj->CachedChildrenIncludingIgnored().empty()) {
    return;
  }

  // Clear children of ancestors in order to ensure this detached object is not
  // cached in an ancestor's list of children:
  // Any ancestor up to the first included ancestor can contain the now-detached
  // child in it's cached children, and therefore must update children.
  AXObject* ax_ancestor = ChildrenChanged(obj->CachedParentObject());
  if (!ax_ancestor) {
    return;
  }

  SANITIZER_CHECK(!IsFrozen())
      << "Attempting to change children on an ancestor is dangerous during "
         "serialization, because the ancestor may have already been "
         "visited. Reaching this line indicates that AXObjectCacheImpl did "
         "not handle a signal and call ChildrenChanged() earlier."
      << "\nChild: " << obj->ToString(true) << "\nParent: "
      << (obj->CachedParentObject() ? obj->CachedParentObject()->ToString(true)
                                    : "")
      << "\nAncestor: " << ax_ancestor->ToString(true);
}

void AXObjectCacheImpl::ChildrenChangedWithCleanLayout(AXObject* obj) {
  if (AXObject* ax_ancestor_for_notification = InvalidateChildren(obj)) {
    ChildrenChangedWithCleanLayout(ax_ancestor_for_notification->GetNode(),
                                   ax_ancestor_for_notification);
  }
}

AXObject* AXObjectCacheImpl::ChildrenChanged(AXObject* obj) {
  if (AXObject* ax_ancestor_for_notification = InvalidateChildren(obj)) {
    DeferTreeUpdate(TreeUpdateReason::kChildrenChanged,
                    ax_ancestor_for_notification);
    return ax_ancestor_for_notification;
  }
  return nullptr;
}

AXObject* AXObjectCacheImpl::InvalidateChildren(AXObject* obj) {
  if (!obj)
    return nullptr;

  // Clear children of ancestors in order to ensure this detached object is not
  // cached an ancestor's list of children:
  AXObject* ancestor = obj;
  while (ancestor) {
    if (ancestor->NeedsToUpdateChildren() || ancestor->IsDetached())
      return nullptr;  // Processing has already occurred for this ancestor.
    ancestor->SetNeedsToUpdateChildren();

    // Any ancestor up to the first included ancestor can contain the
    // now-detached child in it's cached children, and therefore must update
    // children.
    if (ancestor->LastKnownIsIncludedInTreeValue()) {
      break;
    }

    ancestor = ancestor->CachedParentObject();
  }

  // Only process ChildrenChanged() events on the included ancestor. This allows
  // deduping of ChildrenChanged() occurrences within the same subtree.
  // For example, if a subtree has unincluded children, but included
  // grandchildren have changed, only the root children changed needs to be
  // processed.
  if (!ancestor)
    return nullptr;
  // Don't enqueue a deferred event on the same node more than once.
  if (ancestor->GetNode() &&
      !nodes_with_pending_children_changed_.insert(ancestor->GetNode())
           .is_new_entry) {
    return nullptr;
  }

  // Return ancestor to fire children changed notification on.
  DCHECK(ancestor->LastKnownIsIncludedInTreeValue())
      << "ChildrenChanged() must only be called on included nodes: "
      << ancestor->ToString(true, true);

  return ancestor;
}

void AXObjectCacheImpl::SlotAssignmentWillChange(Node* node) {
  // Use SafeGet(), because right before slot assignment is a dangerous time to
  // test whether the slot must be invalidated, because this currently requires
  // looking at the <slot> children in
  // IsShadowContentRelevantForAccessibility(), resulting in an infinite loop
  // as looking at the children causes slot assignment to be recalculated.
  // TODO(accessibility) In the future this may be simplified.
  // See crbug.com/1219311.
  ChildrenChanged(SafeGet(node));
}

void AXObjectCacheImpl::ChildrenChanged(Node* node) {
  // Use SafeGet() because there is no guarantee that layout is clean right now.
  ChildrenChanged(SafeGet(node));
}

// ChildrenChanged gets called a lot. For the accessibility tests that
// measure performance when many nodes change, ChildrenChanged can be
// called tens of thousands of times. We need to balance catching changes
// for this metric with not slowing the perf bots down significantly.
// Tracing every 25 calls is an attempt at achieving that balance and
// may need to be adjusted further.
constexpr int kChildrenChangedTraceFrequency = 25;

void AXObjectCacheImpl::ChildrenChanged(const LayoutObject* layout_object) {
  static int children_changed_counter = 0;
  if (++children_changed_counter % kChildrenChangedTraceFrequency == 0) {
    TRACE_EVENT0("accessibility",
                 "AXObjectCacheImpl::ChildrenChanged(LayoutObject)");
  }

  if (!layout_object)
    return;

  // Ensure that this object is touched, so that Get() can Invalidate() it if
  // necessary, e.g. to change whether it's an AXNodeObject <--> AXLayoutObject.
  Get(layout_object);

  // Update using nearest node (walking ancestors if necessary).
  Node* node = GetClosestNodeForLayoutObject(layout_object);
  if (!node)
    return;

  ChildrenChanged(node);
}

void AXObjectCacheImpl::ChildrenChanged(AccessibleNode* accessible_node) {
  DCHECK(accessible_node);
  ChildrenChanged(Get(accessible_node));
}

void AXObjectCacheImpl::ChildrenChangedWithCleanLayout(Node* node) {
  ChildrenChangedWithCleanLayout(node, Get(node));
}

void AXObjectCacheImpl::ChildrenChangedWithCleanLayout(Node* optional_node,
                                                       AXObject* obj) {
  if (HTMLMapElement* map_element = DynamicTo<HTMLMapElement>(optional_node)) {
    obj = GetAXImageForMap(*map_element);
    if (!obj)
      return;
    optional_node = obj->GetNode();
  }
  if (obj ? obj->IsDetached() : !optional_node)
    return;

#if DCHECK_IS_ON()
  if (obj && optional_node) {
    DCHECK_EQ(obj->GetNode(), optional_node);
    DCHECK_EQ(obj, SafeGet(optional_node));
  }
  Document* document = obj ? obj->GetDocument() : &optional_node->GetDocument();
  DCHECK(document);
  DCHECK(document->Lifecycle().GetState() >= DocumentLifecycle::kLayoutClean)
      << "Unclean document at lifecycle " << document->Lifecycle().ToString();
#endif  // DCHECK_IS_ON()

  if (obj) {
    obj->ChildrenChangedWithCleanLayout();
    // TODO(accessibility) Only needed for <select> size changes.
    // This can turn into a DCHECK if the shadow DOM is used for <select>
    // elements instead of AXMenuList* and AXListBox* classes.
    if (obj->IsDetached())
      return;
  }

  if (optional_node)
    relation_cache_->UpdateRelatedTree(optional_node, obj);

  TableCellRoleMaybeChanged(optional_node);
}

void AXObjectCacheImpl::UpdateTreeIfNeeded() {
  if (!RuntimeEnabledFeatures::AccessibilityEagerAXTreeUpdateEnabled()) {
    return;
  }

  DCHECK(!updating_tree_);
  if (Root()->HasDirtyDescendants()) {
    base::AutoReset<bool> updating(&updating_tree_, true);
    HeapDeque<Member<AXObject>> objects_to_process;
    objects_to_process.push_back(Root());
    while (!objects_to_process.empty()) {
      AXObject* obj = objects_to_process.front();
      objects_to_process.pop_front();
      if (obj->IsDetached()) {
        continue;
      }
      obj->UpdateChildrenIfNecessary();
      if (obj->HasDirtyDescendants()) {
        obj->SetHasDirtyDescendants(false);
        for (auto& child : obj->ChildrenIncludingIgnored()) {
          objects_to_process.push_back(child);
        }
      }
    }
  }

#if EXPENSIVE_DCHECKS_ARE_ON()
  for (const auto& entry : objects_) {
    const AXObject* object = entry.value;
    DCHECK(!object->IsDetached());
    DCHECK(object->GetDocument());
    DCHECK(object->GetDocument()->GetFrame())
        << "An object in a closed document should have been removed:"
        << "\n* Object: " << object->ToString(true, true);
    DCHECK(!object->IsMissingParent())
        << "No object should be missing its parent: "
        << "\n* Object: " << object->ToString(true, true)
        << "\n* Computed parent: "
        << (object->ComputeParent() ? object->ComputeParent()->ToString(true)
                                    : "not found");
    AXObject* included_parent = object->ParentObjectIncludedInTree();
    DCHECK(!object->HasDirtyDescendants())
        << "No subtrees should be flagged as needing updates at this point:"
        << "\n* Object: " << object->ToString(true) << "\n* Included parent: "
        << (included_parent ? included_parent->ToString(true) : "");
    DCHECK(!object->NeedsToUpdateChildren())
        << "No children in the tree should require an update at this point: "
        << "\n* Object: " << object->ToString(true) << "\n* Included parent: "
        << (included_parent ? included_parent->ToString(true) : "");
    DCHECK(!object->NeedsToUpdateCachedValues())
        << "No cached values should require an update at this point: "
        << "\n* Object: " << object->ToString(true) << "\n* Included parent: "
        << (included_parent ? included_parent->ToString(true) : "");
  }
#endif
}

void AXObjectCacheImpl::ProcessDeferredAccessibilityEvents(Document& document) {
  if (IsPopup(document)) {
    // Only process popup document together with main document.
    DCHECK_EQ(&document, GetPopupDocumentIfShowing());
    // Since a change occurred in the popup, processing of both documents will
    // be needed. A visual update on the main document will force this.
    ScheduleAXUpdate();
    return;
  }

  DCHECK_EQ(document, GetDocument());

  DCHECK(!processing_deferred_events_);

  if (tree_updates_paused_) {
    LOG(INFO) << "Accessibility tree updates will be resumed after rebuilding "
                 "the tree from root";
    MarkDocumentDirty();
    tree_updates_paused_ = false;
    return;
  }

  // If MarkDocumentDirty() was called, do it now, so that the entire tree is
  // invalidated before updating it.
  if (mark_all_dirty_) {
    MarkDocumentDirtyWithCleanLayout();
  }

  if (IsDirty()) {
    if (GetPopupDocumentIfShowing()) {
      UpdateLifecycleIfNeeded(*GetPopupDocumentIfShowing());
      ProcessDeferredAccessibilityEventsImpl(*GetPopupDocumentIfShowing());
    }
    ProcessDeferredAccessibilityEventsImpl(document);
  }

#if BUILDFLAG(IS_ANDROID)
  // On Android, the inline textboxes of focused editable subtrees are always
  // loaded, but only if inline text boxes are enabled.
  if (ax_mode_.has_mode(ui::AXMode::kInlineTextBoxes)) {
    AXObject* focus = FocusedObject();
    if (focus && focus->IsEditableRoot()) {
      focus->LoadInlineTextBoxes();
    }
  }
#endif

  // Build out tree, such that each node has computed its children.
  if (RuntimeEnabledFeatures::AccessibilityEagerAXTreeUpdateEnabled()) {
    UpdateTreeIfNeeded();
  }

  // Check whether there are dirty objects ready to be serialized.
  // TODO(accessibility) It's a bit confusing that this can be true when the
  // IsDirty() is false, but this is the case for objects marked dirty from
  // RenderAccessibilityImpl, e.g. for the kEndOfTest event.
  if (HasDirtyObjects()) {
    if (auto* client = GetWebLocalFrameClient())
      client->AXReadyCallback();
  }

  // Accessibility is now clean for both documents: AXObjects can be safely
  // traversed and AXObject's properties can be safely fetched.
  // TODO(accessibility) Now that both documents are always processed at the
  // same time, consider modifying the InspectorAccessibilityAgent so that only
  // the callback for the main document is needed.
  for (auto agent : agents_) {
    agent->AXReadyCallback(document);
    if (GetPopupDocumentIfShowing())
      agent->AXReadyCallback(*GetPopupDocumentIfShowing());
  }
}

void AXObjectCacheImpl::ProcessDeferredAccessibilityEventsImpl(
    Document& document) {
  TRACE_EVENT0("accessibility", "ProcessDeferredAccessibilityEvents");

  DCHECK(GetDocument().IsAccessibilityEnabled())
      << "ProcessDeferredAccessibilityEvents should not perform work when "
         "accessibility is not enabled."
      << "\n* IsPopup? " << IsPopup(document);

  SCOPED_UMA_HISTOGRAM_TIMER(
      "Accessibility.Performance.ProcessDeferredAccessibilityEvents");

#if DCHECK_IS_ON()
  int loop_counter = 0;
#endif

  base::AutoReset<bool> processing(&processing_deferred_events_, true);

  do {
    // Destroy and recreate any objects which are no longer valid, for example
    // they used AXNodeObject and now must be an AXLayoutObject, or vice-versa.
    // Also fires children changed on the parent of these nodes.
    ProcessInvalidatedObjects(document);

    // Call the queued callback methods that do processing which must occur when
    // layout is clean. These callbacks are stored in
    // tree_update_callback_queue_, and have names like
    // FooBarredWithCleanLayout().
    ProcessCleanLayoutCallbacks(document);

    // Changes to ids or aria-owns may have resulted in queued up relation
    // cache work; do that now.
    relation_cache_->ProcessUpdatesWithCleanLayout();

    // Keep going if there are more ids to invalidate or children changes to
    // process from previous steps. For example, a display locked
    // (content-visibility:auto) element could be invalidated as it is scrolled
    // in or out of view, causing Invalidate() to add it to invalidated_ids_.
    // As ProcessInvalidatedObjects() refreshes the objectt and calls
    // ChildrenChanged() on the parent, more objects may be invalidated, or
    // more objects may have children changed called on them.
#if DCHECK_IS_ON()
    DCHECK_LE(++loop_counter, 100) << "Probable infinite loop detected.";
#endif
  } while (!nodes_with_pending_children_changed_.empty() ||
           !GetInvalidatedIds(document).empty());

  // Send events to RenderAccessibilityImpl, which serializes them and then
  // sends the serialized events and dirty objects to the browser process.
  PostNotifications(document);
}

bool AXObjectCacheImpl::IsMainDocumentDirty() const {
  return !tree_update_callback_queue_main_.empty() ||
         !notifications_to_post_main_.empty() || !invalidated_ids_main_.empty();
}

bool AXObjectCacheImpl::IsPopupDocumentDirty() const {
  if (!popup_document_)
    return false;
  return !tree_update_callback_queue_popup_.empty() ||
         !notifications_to_post_popup_.empty() ||
         !invalidated_ids_popup_.empty();
}

bool AXObjectCacheImpl::IsDirty() {
  if (IsMainDocumentDirty() || IsPopupDocumentDirty() ||
      relation_cache_->IsDirty()) {
    return true;
  }
  DCHECK(RuntimeEnabledFeatures::AccessibilityEagerAXTreeUpdateEnabled() ||
         !Root()->HasDirtyDescendants());
  if (RuntimeEnabledFeatures::AccessibilityEagerAXTreeUpdateEnabled()) {
    if (Root()->NeedsToUpdateChildren() || Root()->HasDirtyDescendants()) {
      return true;
    }
  }
  return false;
}

void AXObjectCacheImpl::EmbeddingTokenChanged(HTMLFrameOwnerElement* element) {
  if (!element)
    return;

  MarkElementDirty(element);
}

bool AXObjectCacheImpl::IsPopup(Document& document) const {
  // There are 1-2 documents per AXObjectCache: the main document and
  // sometimes a popup document.
  int is_popup = document != GetDocument();
#if DCHECK_IS_ON()
  if (is_popup) {
    // Verify that the popup document's owner is the main document.
    LocalFrame* frame = document.GetFrame();
    DCHECK(frame);
    Element* popup_owner = frame->PagePopupOwner();
    DCHECK(popup_owner);
    DCHECK_EQ(popup_owner->GetDocument(), GetDocument())
        << "The popup document's owner should be in the main document.";
    Page* main_page = GetDocument().GetPage();
    DCHECK(main_page);
    DCHECK_EQ(&document, popup_document_);
  }
#endif
  return is_popup;
}

HashSet<AXID>& AXObjectCacheImpl::GetInvalidatedIds(Document& document) {
  return IsPopup(document) ? invalidated_ids_popup_ : invalidated_ids_main_;
}

AXObjectCacheImpl::TreeUpdateCallbackQueue&
AXObjectCacheImpl::GetTreeUpdateCallbackQueue(Document& document) {
  return IsPopup(document) ? tree_update_callback_queue_popup_
                           : tree_update_callback_queue_main_;
}

HeapVector<Member<AXObjectCacheImpl::AXEventParams>>&
AXObjectCacheImpl::GetNotificationsToPost(Document& document) {
  return IsPopup(document) ? notifications_to_post_popup_
                           : notifications_to_post_main_;
}

void AXObjectCacheImpl::ProcessInvalidatedObjects(Document& document) {
  // Create a new object with the same AXID as the old one.
  // Currently only supported for objects with a backing node.
  // Returns the new object.
  auto refresh = [this](AXObject* current) {
    DCHECK(current);
    Node* node = current->GetNode();
    DCHECK(node) << "Refresh() is currently only supported for objects "
                    "with a backing node.";
    bool is_ax_layout_object = current->GetLayoutObject();
    bool will_be_ax_layout_object =
        node->GetLayoutObject() &&
        IsLayoutObjectRelevantForAccessibility(*node->GetLayoutObject()) &&
        !IsDisplayLocked(node);
    if (is_ax_layout_object == will_be_ax_layout_object)
      return static_cast<AXObject*>(nullptr);  // No change in the AXObject.

    // When a pseudo element loses its layout, destroy all of the descendant
    // objects (there were likely some that could not be individually
    // invalidated because only AXObjects with a node can be invalidated, and
    // pseudo element descendants to not generally have a node).
    if (!will_be_ax_layout_object && node->IsPseudoElement()) {
      RemoveIncludedSubtree(current, /* remove_root */ false);
    }

    AXID retained_axid = current->AXObjectID();
    // Remove from relevant maps, but not from relation cache, as the relations
    // between AXIDs will still be the same.
    node_object_mapping_.erase(node);
    if (is_ax_layout_object) {
      layout_object_mapping_.erase(current->GetLayoutObject());
    } else {
      DCHECK(will_be_ax_layout_object);
      DCHECK(node->GetLayoutObject());
      DCHECK(!layout_object_mapping_.Contains(node->GetLayoutObject()))
          << node << " " << node->GetLayoutObject();
    }

    ChildrenChangedOnAncestorOf(current);
    current->Detach();

    // TODO(accessibility) We don't use the return value, can we use .erase()
    // and it will still make sure that the object is cleaned up?
    objects_.Take(retained_axid);
    // Do not pass in the previous parent. It may not end up being the same,
    // e.g. in the case of a <select> option where the select changed size.
    // TODO(accessibility) That may be the only example of this, in which case
    // it could be handled in RoleChangedWithCleanLayout(), and the cached
    // parent could be used.
    AXObject* new_object = CreateAndInit(
        node, node->GetLayoutObject(),
        AXObject::ComputeNonARIAParent(*this, node), retained_axid);
    if (new_object) {
      // Any owned objects need to reset their parent_ to point to the
      // new object.
      if (AXObject::HasARIAOwns(DynamicTo<Element>(node)) &&
          AXRelationCache::IsValidOwner(new_object)) {
        relation_cache_->UpdateAriaOwnsWithCleanLayout(new_object, true);
      }
    } else {
      // Failed to create, so remove object completely.
      RemoveReferencesToAXID(retained_axid);
    }

    return new_object;
  };

  // ChildrenChanged() calls from below work may invalidate more objects.
  // Thereore, work from a separate list of ids, allowing new invalidated_ids.
  HashSet<AXID> old_invalidated_ids;
  old_invalidated_ids.swap(GetInvalidatedIds(document));
  for (AXID ax_id : old_invalidated_ids) {
    AXObject* object = ObjectFromAXID(ax_id);
    if (!object || object->IsDetached())
      continue;
    DCHECK_EQ(object->GetDocument(), &document);
    bool was_included = object->LastKnownIsIncludedInTreeValue();

#if defined(AX_FAIL_FAST_BUILD)
    bool did_use_layout_object_traversal =
        object->ShouldUseLayoutObjectTraversalForChildren();
#endif

    // Invalidate children on the first available non-detached parent that is
    // included in the tree. Sometimes a cached parent is detached because
    // an object was detached in the middle of the tree, and cached parents
    // are not corrected until the call to UpdateChildrenIfNecessary() below.
    AXObject* parent = object;
    while (true) {
      AXObject* candidate_parent = parent->CachedParentObject();
      if (!candidate_parent || candidate_parent->IsDetached()) {
        // The cached parent pointed to a detached AXObject. Compute a new
        // candidate parent and repair the cached parent now, so that
        // refreshing and initializing the new object can occur (a parent is
        // required).
        candidate_parent = parent->ComputeParent();
        if (candidate_parent)
          parent->SetParent(candidate_parent);
      }

      parent = candidate_parent;
      if (!parent)
        break;  // No higher candidate parent found, will invalidate |parent|.

      // Queue up a ChildrenChanged() call for this parent.
      if (parent->LastKnownIsIncludedInTreeValue())
        break;  // Stop here (otherwise continue to higher ancestor).
    }

    if (!parent) {
      // If no parent is possible, prune from the tree.
      Remove(object, /* notify_parent */ false);
      continue;
    }

    AXObject* new_object = refresh(object);
    bool is_included =
        new_object && new_object->AccessibilityIsIncludedInTree();
    if (is_included) {
      MarkAXObjectDirtyWithCleanLayout(new_object);
    }
    if (was_included != is_included) {
      ChildrenChangedWithCleanLayout(parent);
    }

#if defined(AX_FAIL_FAST_BUILD)
    SANITIZER_CHECK(!new_object ||
                    new_object->ShouldUseLayoutObjectTraversalForChildren() ==
                        did_use_layout_object_traversal)
        << "This should no longer be possible, an object only uses layout "
           "object traversal if it is part of a pseudo element subtree, "
           "and that never changes: "
        << new_object->ToString(true, true);
#endif
  }
}

void AXObjectCacheImpl::ProcessCleanLayoutCallbacks(Document& document) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  UpdateNumTreeUpdatesQueuedBeforeLayoutHistogram();

  TreeUpdateCallbackQueue old_tree_update_callback_queue;
  GetTreeUpdateCallbackQueue(document).swap(old_tree_update_callback_queue);
  nodes_with_pending_children_changed_.clear();
  nodes_with_pending_location_changed_.clear();
  last_value_change_node_ = ui::AXNodeData::kInvalidAXID;

  for (TreeUpdateParams* tree_update : old_tree_update_callback_queue) {
    if (IsTreeUpdateRelevant(document, tree_update)) {
      FireTreeUpdatedEventImmediately(document, tree_update);
    }
  }
}

void AXObjectCacheImpl::PostNotifications(Document& document) {
  HeapVector<Member<AXEventParams>> old_notifications_to_post;
  GetNotificationsToPost(document).swap(old_notifications_to_post);
  for (auto& params : old_notifications_to_post) {
    AXObject* obj = params->target;

    if (!obj || !obj->AXObjectID())
      continue;

    if (obj->IsDetached())
      continue;

    DCHECK_EQ(obj->GetDocument(), &document)
        << "Wrong document in PostNotifications";

    ax::mojom::blink::Event event_type = params->event_type;
    ax::mojom::blink::EventFrom event_from = params->event_from;
    ax::mojom::blink::Action event_from_action = params->event_from_action;
    const BlinkAXEventIntentsSet& event_intents = params->event_intents;
    FireAXEventImmediately(obj, event_type, event_from, event_from_action,
                           event_intents);
  }
}

void AXObjectCacheImpl::PostNotification(const LayoutObject* layout_object,
                                         ax::mojom::blink::Event notification) {
  if (!layout_object)
    return;
  PostNotification(Get(layout_object), notification);
}

void AXObjectCacheImpl::PostNotification(Node* node,
                                         ax::mojom::blink::Event notification) {
  if (!node)
    return;
  PostNotification(Get(node), notification);
}

void AXObjectCacheImpl::EnsurePostNotification(
    Node* node,
    ax::mojom::blink::Event notification) {
  if (!node)
    return;
  PostNotification(GetOrCreate(node), notification);
}

void AXObjectCacheImpl::PostNotification(AXObject* object,
                                         ax::mojom::blink::Event event_type) {
  if (!object || !object->AXObjectID() || object->IsDetached())
    return;

  Document& document = *object->GetDocument();

  // It's possible for FireAXEventImmediately to post another notification.
  // If we're still in the accessibility document lifecycle, fire these events
  // immediately rather than deferring them.
  if (processing_deferred_events_) {
    FireAXEventImmediately(object, event_type, ComputeEventFrom(),
                           active_event_from_action_, ActiveEventIntents());
    return;
  }

  GetNotificationsToPost(document).push_back(
      MakeGarbageCollected<AXEventParams>(
          object, event_type, ComputeEventFrom(), active_event_from_action_,
          ActiveEventIntents()));

  // These events are fired during RunPostLifecycleTasks(),
  // ensure there is a visual update scheduled.
  ScheduleAXUpdate();
}

void AXObjectCacheImpl::ScheduleAXUpdate() const {
  // A visual update will force accessibility to be updated as well.
  // Scheduling visual updates before the document is finished loading can
  // interfere with event ordering. In any case, at least one visual update will
  // occur between now and when the document load is complete.
  if (!GetDocument().IsLoadCompleted())
    return;

  // If there was a document change that doesn't trigger a lifecycle update on
  // its own, (e.g. because it doesn't make layout dirty), make sure we run
  // lifecycle phases to update the computed accessibility tree.
  LocalFrameView* frame_view = GetDocument().View();
  Page* page = GetDocument().GetPage();
  if (!frame_view || !page)
    return;

  if (!frame_view->CanThrottleRendering() &&
      !GetDocument().GetPage()->Animator().IsServicingAnimations()) {
    page->Animator().ScheduleVisualUpdate(GetDocument().GetFrame());
  }
}

bool AXObjectCacheImpl::IsTreeUpdateRelevant(Document& document,
                                             TreeUpdateParams* tree_update) {
  if (tree_update->node) {
    Document& tree_update_document = tree_update->node->GetDocument();
    return document == tree_update_document && tree_update->node->isConnected();
  }

  if (!tree_update->axid) {
    // No node and no AXID means that it was a node update, but the
    // WeakMember<Node> is no longer available.
    return false;
  }

  AXObject* ax_obj = ObjectFromAXID(tree_update->axid);
  if (!ax_obj) {
    return false;
  }

  if (ax_obj->GetNode() && !ax_obj->GetNode()->isConnected()) {
    return false;
  }

  Document* tree_update_document = ax_obj->GetDocument();
  return document == *tree_update_document;
}

void AXObjectCacheImpl::FireTreeUpdatedEventImmediately(
    Document& document,
    TreeUpdateParams* tree_update) {
  DCHECK(processing_deferred_events_);

  base::AutoReset<ax::mojom::blink::EventFrom> event_from_resetter(
      &active_event_from_, tree_update->event_from);
  base::AutoReset<ax::mojom::blink::Action> event_from_action_resetter(
      &active_event_from_action_, tree_update->event_from_action);
  ScopedBlinkAXEventIntent defered_event_intents(
      tree_update->event_intents.AsVector(), &document);

  if (tree_update->axid) {
    DCHECK(!tree_update->node)
        << "Cannot have both a node and AXID for a tree update.";
    AXObject* ax_object = ObjectFromAXID(tree_update->axid);
    if (!ax_object) {
      return;  // AXObject was destroyed before we got to the event.
    }

    CHECK(!ax_object->GetNode() || ax_object->GetNode()->isConnected());

    // Update cached attributes for all changed nodes before serialization,
    // because updating ignored/included can cause tree structure changes, and
    // the tree structure needs to be stable before serialization begins.
    ax_object->UpdateCachedAttributeValuesIfNeeded();
    if (ax_object->IsDetached()) {
      return;
    }

    switch (tree_update->update_reason) {
      case TreeUpdateReason::kChildrenChanged:
        ChildrenChangedWithCleanLayout(ax_object->GetNode(), ax_object);
        break;
      case TreeUpdateReason::kMarkAXObjectDirty:
        MarkAXObjectDirtyWithCleanLayout(ax_object);
        break;
      case TreeUpdateReason::kMarkAXSubtreeDirty:
        MarkAXSubtreeDirtyWithCleanLayout(ax_object);
        break;
      case TreeUpdateReason::kTextChangedFromTextChangedAXObject:
        TextChangedWithCleanLayout(ax_object->GetNode(), ax_object);
        break;
      case TreeUpdateReason::kTextOffsetsChanged:
        TextOffsetsChangedWithCleanLayout(ax_object);
        break;
      default:
        NOTREACHED() << "Update reason not handled: "
                     << static_cast<int>(tree_update->update_reason);
    }
    return;
  }

  // This is a Node Event.
  Node* node = tree_update->node;
  DCHECK(node);
  CHECK(node->isConnected());

  AXObject* ax_object = GetOrCreate(tree_update->node);
  if (!ax_object) {
    return;
  }
  DCHECK(!ax_object->IsDetached());

  ax_object->UpdateCachedAttributeValuesIfNeeded();
  if (ax_object->IsDetached()) {
    return;
  }

  switch (tree_update->update_reason) {
    case TreeUpdateReason::kActiveDescendantChanged:
      HandleActiveDescendantChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kAriaExpandedChanged:
      HandleAriaExpandedChangeWithCleanLayout(node);
      break;
    case TreeUpdateReason::kAriaOwnsChanged:
      AriaOwnsChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kAriaPressedChanged:
      HandleAriaPressedChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kAriaSelectedChanged:
      HandleAriaSelectedChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kDidHideMenuListPopup:
      DidHideMenuListPopupWithCleanLayout(node);
      break;
    case TreeUpdateReason::kDidShowMenuListPopup:
      DidShowMenuListPopupWithCleanLayout(node);
      break;
    case TreeUpdateReason::kEditableTextContentChanged:
      HandleEditableTextContentChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kFocusableChanged:
      FocusableChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kIdChanged:
      IdChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kInvalidateCachedValuesOnSubtree:
      InvalidateCachedValuesOnSubtreeWithCleanLayout(node);
      break;
    case TreeUpdateReason::kLabelChanged:
      LabelChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kMarkDirtyFromHandleLayout:
    case TreeUpdateReason::kMarkDirtyFromHandleScroll:
    case TreeUpdateReason::kMarkDirtyFromRemove:
      EnsureMarkDirtyWithCleanLayout(node);
      break;
    case TreeUpdateReason::kNameAttributeChanged:
      HandleNameAttributeChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kNodeGainedFocus:
      HandleNodeGainedFocusWithCleanLayout(node);
      break;
    case TreeUpdateReason::kNodeLostFocus:
      HandleNodeLostFocusWithCleanLayout(node);
      break;
    case TreeUpdateReason::kPostNotificationFromHandleLoadComplete:
    case TreeUpdateReason::kPostNotificationFromHandleLoadStart:
      EnsurePostNotification(node, tree_update->event);
      break;
    case TreeUpdateReason::kRemoveValidationMessageObjectFromFocusedUIElement:
    case TreeUpdateReason::
        kRemoveValidationMessageObjectFromValidationMessageObject:
      RemoveValidationMessageObjectWithCleanLayout(node);
      break;
    case TreeUpdateReason::kRoleChangeFromAriaHasPopup:
    case TreeUpdateReason::kRoleChangeFromRoleOrType:
      HandleRoleChangeWithCleanLayout(node);
      break;
    case TreeUpdateReason::kRoleMaybeChangedFromEventListener:
    case TreeUpdateReason::kRoleMaybeChangedFromHref:
      HandleRoleMaybeChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kSectionOrRegionRoleMaybeChangedFromLabel:
    case TreeUpdateReason::kSectionOrRegionRoleMaybeChangedFromTitle:
      SectionOrRegionRoleMaybeChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kTextChangedFromTextChangedNode:
      TextChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kTextMarkerDataAdded:
      HandleTextMarkerDataAddedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kUpdateActiveMenuOption:
      HandleUpdateActiveMenuOptionWithCleanLayout(node);
      break;
    case TreeUpdateReason::kUpdateCacheAfterNodeIsAttached:
      UpdateCacheAfterNodeIsAttachedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kUpdateTableRole:
      UpdateTableRoleWithCleanLayout(node);
      break;
    case TreeUpdateReason::kUseMapAttributeChanged:
      HandleUseMapAttributeChangedWithCleanLayout(node);
      break;
    case TreeUpdateReason::kValidationMessageVisibilityChanged:
      HandleValidationMessageVisibilityChangedWithCleanLayout(node);
      break;
    default:
      NOTREACHED() << "Update reason not handled: "
                   << static_cast<int>(tree_update->update_reason);
  }
}

void AXObjectCacheImpl::FireAXEventImmediately(
    AXObject* obj,
    ax::mojom::blink::Event event_type,
    ax::mojom::blink::EventFrom event_from,
    ax::mojom::blink::Action event_from_action,
    const BlinkAXEventIntentsSet& event_intents) {
#if DCHECK_IS_ON()
  // Make sure that we're not in the process of being laid out. Notifications
  // should only be sent after the LayoutObject has finished
  DCHECK(GetDocument().Lifecycle().GetState() !=
         DocumentLifecycle::kInPerformLayout);

  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();
#endif  // DCHECK_IS_ON()

  PostPlatformNotification(obj, event_type, event_from, event_from_action,
                           event_intents);
}

bool AXObjectCacheImpl::IsAriaOwned(const AXObject* object) const {
  return relation_cache_->IsAriaOwned(object);
}

AXObject* AXObjectCacheImpl::ValidatedAriaOwner(const AXObject* object) const {
  return relation_cache_->ValidatedAriaOwner(object);
}

void AXObjectCacheImpl::ValidatedAriaOwnedChildren(
    const AXObject* owner,
    HeapVector<Member<AXObject>>& owned_children) {
  DCHECK(GetDocument().Lifecycle().GetState() >=
         DocumentLifecycle::kLayoutClean);
  relation_cache_->ValidatedAriaOwnedChildren(owner, owned_children);
}

bool AXObjectCacheImpl::MayHaveHTMLLabel(const HTMLElement& elem) {
  // Return false if this type of element will not accept a <label for> label.
  if (!elem.IsLabelable())
    return false;

  // Return true if a <label for> pointed to this element at some point.
  if (relation_cache_->MayHaveHTMLLabelViaForAttribute(elem))
    return true;

  // Return true if any amcestor is a label, as in <label><input></label>.
  return Traversal<HTMLLabelElement>::FirstAncestor(elem);
}

void AXObjectCacheImpl::CheckedStateChanged(Node* node) {
  PostNotification(node, ax::mojom::blink::Event::kCheckedStateChanged);
}

void AXObjectCacheImpl::ListboxOptionStateChanged(HTMLOptionElement* option) {
  PostNotification(option, ax::mojom::Event::kCheckedStateChanged);
}

void AXObjectCacheImpl::ListboxSelectedChildrenChanged(
    HTMLSelectElement* select) {
  PostNotification(select, ax::mojom::Event::kSelectedChildrenChanged);
}

void AXObjectCacheImpl::ListboxActiveIndexChanged(HTMLSelectElement* select) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  auto* ax_object = DynamicTo<AXListBox>(Get(select));
  if (!ax_object)
    return;

  ax_object->ActiveIndexChanged();
}

void AXObjectCacheImpl::SetMenuListOptionsBounds(
    HTMLSelectElement* select,
    const WTF::Vector<gfx::Rect>& options_bounds) {
  auto* ax_object = DynamicTo<AXMenuList>(Get(select));
  if (!ax_object) {
    return;
  }

  ax_object->SetOptionsBounds(options_bounds);
}

// This is called when the actual style of an object changed, which can occur in
// script-based animations as opposed to more automated animations, e.g. via CSS
// or SVG animation.
void AXObjectCacheImpl::LocationChanged(const LayoutObject* layout_object) {
  // No need to send this notification if the object is aria-hidden.
  // Note that if the node is ignored for other reasons, it still might
  // be important to send this notification if any of its children are
  // visible - but in the case of aria-hidden we can safely ignore it.
  // Use CachedIsAriaHidden() instead of IsAriaHidden() because layout is not
  // clean here, and it's better to do the optimization up front. This is okay
  // because if the cached aria-hidden becomes stale, then the entire subtree
  // will be invalidated anyway.
  AXObject* obj = Get(layout_object);
  if (obj) {
    if (obj->CachedIsAriaHidden())
      return;
    if (!nodes_with_pending_location_changed_.insert(obj->AXObjectID())
             .is_new_entry) {
      return;
    }
  }

  PostNotification(layout_object, ax::mojom::Event::kLocationChanged);
}

void AXObjectCacheImpl::ImageLoaded(const LayoutObject* layout_object) {
  MarkElementDirty(layout_object->GetNode());
}

void AXObjectCacheImpl::HandleClicked(Node* node) {
  if (AXObject* obj = Get(node))
    PostNotification(obj, ax::mojom::Event::kClicked);
}

void AXObjectCacheImpl::HandleAttributeChanged(
    const QualifiedName& attr_name,
    AccessibleNode* accessible_node) {
  if (!accessible_node)
    return;
  MarkAXObjectDirty(Get(accessible_node));
}

void AXObjectCacheImpl::FinishedParsingTable(HTMLTableElement* table) {
  // The data table heuristic can change from false to true as a table's
  // children are parsed; but it will never change from true to false.
  if (AXObject* ax_object = SafeGet(table)) {
    if (ax_object->RoleValue() == ax::mojom::blink::Role::kLayoutTable) {
      DeferTreeUpdate(TreeUpdateReason::kUpdateTableRole, table);
    }
  }
}

void AXObjectCacheImpl::UpdateTableRoleWithCleanLayout(Node* table) {
  if (AXObject* ax_table = Get(table)) {
    if (ax_table->RoleValue() == ax::mojom::blink::Role::kLayoutTable &&
        ax_table->IsDataTable()) {
      HandleRoleChangeWithCleanLayout(table);
    }
  }
}

void AXObjectCacheImpl::HandleAriaExpandedChangeWithCleanLayout(Node* node) {
  if (!node)
    return;

  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  DCHECK(!node->GetDocument().NeedsLayoutTreeUpdateForNode(*node));
  if (AXObject* obj = GetOrCreate(node))
    obj->HandleAriaExpandedChanged();
}

void AXObjectCacheImpl::HandleAriaPressedChangedWithCleanLayout(Node* node) {
  AXObject* ax_object = Get(node);
  if (!ax_object)
    return;

  ax::mojom::blink::Role previous_role = ax_object->RoleValue();
  bool was_toggle_button =
      previous_role == ax::mojom::blink::Role::kToggleButton;
  bool is_toggle_button = ax_object->HasAttribute(html_names::kAriaPressedAttr);

  if (was_toggle_button != is_toggle_button)
    HandleRoleChangeWithCleanLayout(node);
  else
    PostNotification(node, ax::mojom::blink::Event::kCheckedStateChanged);
}

// In single selection containers, selection follows focus, so a selection
// changed event must be fired. This ensures the AT is notified that the
// selected state has changed, so that it does not read "unselected" as
// the user navigates through the items. The event generator will handle
// the correct events as long as the old and newly selected objects are marked
// dirty.
void AXObjectCacheImpl::HandleAriaSelectedChangedWithCleanLayout(Node* node) {
  DCHECK(node);
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  DCHECK(!node->GetDocument().NeedsLayoutTreeUpdateForNode(*node));
  AXObject* obj = Get(node);
  if (!obj)
    return;

  // Mark the previous selected item dirty if it was selected viaa "selection
  // follows focus".
  if (last_selected_from_active_descendant_)
    MarkElementDirtyWithCleanLayout(last_selected_from_active_descendant_);

  // Mark the newly selected item dirty, and track it for use in the future.
  MarkAXObjectDirtyWithCleanLayout(obj);
  if (obj->IsSelectedFromFocus())
    last_selected_from_active_descendant_ = node;

  PostNotification(obj, ax::mojom::Event::kCheckedStateChanged);

  AXObject* listbox = obj->ParentObjectUnignored();
  if (listbox && listbox->RoleValue() == ax::mojom::Role::kListBox) {
    // Ensure listbox options are in sync as selection status may have changed
    MarkAXSubtreeDirty(listbox);
    PostNotification(listbox, ax::mojom::Event::kSelectedChildrenChanged);
  }
}

void AXObjectCacheImpl::HandleNodeLostFocusWithCleanLayout(Node* node) {
  DCHECK(node);
  DCHECK(!node->GetDocument().NeedsLayoutTreeUpdateForNode(*node));
  AXObject* obj = Get(node);
  if (!obj)
    return;

  TRACE_EVENT1("accessibility",
               "AXObjectCacheImpl::HandleNodeLostFocusWithCleanLayout", "id",
               obj->AXObjectID());
  PostNotification(obj, ax::mojom::Event::kBlur);

  if (AXObject* active_descendant = obj->ActiveDescendant()) {
    if (active_descendant->IsSelectedFromFocusSupported())
      HandleAriaSelectedChangedWithCleanLayout(active_descendant->GetNode());
  }
}

void AXObjectCacheImpl::HandleNodeGainedFocusWithCleanLayout(Node* node) {
  node = FocusedElement();  // Needs to get this with clean layout.
  if (!node || !node->GetDocument().View())
    return;

  AXObject* obj = GetOrCreateFocusedObjectFromNode(node);
  if (!obj)
    return;

  TRACE_EVENT1("accessibility",
               "AXObjectCacheImpl::HandleNodeGainedFocusWithCleanLayout", "id",
               obj->AXObjectID());
  PostNotification(obj, ax::mojom::Event::kFocus);

  if (AXObject* active_descendant = obj->ActiveDescendant()) {
    if (active_descendant->IsSelectedFromFocusSupported())
      HandleAriaSelectedChangedWithCleanLayout(active_descendant->GetNode());
  }
}

// This might be the new target of a relation. Handle all possible cases.
void AXObjectCacheImpl::MaybeNewRelationTarget(Node& node, AXObject* obj) {
  // Track reverse relations
  relation_cache_->UpdateRelatedTree(&node, obj);

  if (!obj)
    return;

  DCHECK_EQ(obj->GetNode(), &node);

  // Process completed relations for new ids.
  if (Element* element = DynamicTo<Element>(node)) {
    const AtomicString& id = element->GetIdAttribute();
    if (!id.IsNull()) {
      relation_cache_->ProcessCompletedRelationsForNewId(id);
    }
  }

  // Check whether aria-activedescendant on the focused object points to
  // |obj|. If so, fire activedescendantchanged event now. This is only for
  // ARIA active descendants, not in a native control like a listbox, which
  // has its own initial active descendant handling.
  Node* focused_node = document_->FocusedElement();
  if (focused_node) {
    AXObject* focus = Get(focused_node);
    if (focus && focus->GetAOMPropertyOrARIAAttribute(
                     AOMRelationProperty::kActiveDescendant) == &node) {
      focus->HandleActiveDescendantChanged();
    }
  }
}

void AXObjectCacheImpl::HandleActiveDescendantChangedWithCleanLayout(
    Node* node) {
  DCHECK(node);
  DCHECK(!node->GetDocument().NeedsLayoutTreeUpdateForNode(*node));

  if (Element* element = DynamicTo<Element>(node)) {
    if (auto& value = AccessibleNode::GetPropertyOrARIAAttributeValue(
            element, AOMRelationProperty::kActiveDescendant)) {
      relation_cache_->UpdateReverseActiveDescendantRelations(node, value);
    }
  }

  if (AXObject* obj = GetOrCreate(node))
    obj->HandleActiveDescendantChanged();
}

// A <section> or role=region uses the region role if and only if it has a name.
void AXObjectCacheImpl::SectionOrRegionRoleMaybeChangedWithCleanLayout(
    Node* node) {
  TextChangedWithCleanLayout(node);
  Element* element = To<Element>(node);
  AXObject* ax_object = Get(element);
  if (!ax_object)
    return;

  // Require <section> or role="region" markup.
  if (!element->HasTagName(html_names::kSectionTag) &&
      ax_object->RawAriaRole() != ax::mojom::blink::Role::kRegion) {
    return;
  }

  HandleRoleMaybeChangedWithCleanLayout(element);
}

void AXObjectCacheImpl::TableCellRoleMaybeChanged(Node* node) {
  if (!node) {
    return;
  }
  // The role for a table cell depends in complex ways on multiple of its
  // siblings (see DecideRoleFromSiblings). Rather than attempt to reproduce
  // that logic here for invalidation, just recompute the role of all siblings
  // when new table cells are added.
  if (auto* cell = DynamicTo<HTMLTableCellElement>(node)) {
    for (auto* prev = LayoutTreeBuilderTraversal::PreviousSibling(*cell); prev;
         prev = LayoutTreeBuilderTraversal::PreviousSibling(*prev)) {
      HandleRoleMaybeChangedWithCleanLayout(prev);
    }
    HandleRoleMaybeChangedWithCleanLayout(cell);
    for (auto* next = LayoutTreeBuilderTraversal::NextSibling(*cell); next;
         next = LayoutTreeBuilderTraversal::PreviousSibling(*next)) {
      HandleRoleMaybeChangedWithCleanLayout(next);
    }
  }
}

void AXObjectCacheImpl::HandleRoleMaybeChangedWithCleanLayout(Node* node) {
  if (AXObject* obj = GetOrCreate(node)) {
    // If role would stay the same, do nothing.
    if (obj->RoleValue() == obj->DetermineAccessibilityRole()) {
      return;
    }

    HandleRoleChangeWithCleanLayout(node);
  }
}

// Be as safe as possible about changes that could alter the accessibility role,
// as this may require a different subclass of AXObject.
// Role changes are disallowed by the spec but we must handle it gracefully, see
// https://www.w3.org/TR/wai-aria-1.1/#h-roles for more information.
void AXObjectCacheImpl::HandleRoleChangeWithCleanLayout(Node* node) {
  if (!node)
    return;  // Virtual AOM node.

  DCHECK(!node->GetDocument().NeedsLayoutTreeUpdateForNode(*node));

  // Remove the current object and make the parent reconsider its children.
  if (AXObject* obj = GetOrCreate(node)) {
    // When the role of `obj` is changed, its AXObject needs to be destroyed and
    // a new one needs to be created in its place.
    if (RolePresentationPropagates(node)) {
      // If role changes on a table, menu, or list invalidate the subtree of
      // objects that may require a specific parent role in order to keep their
      // role. For example, rows and cells require a table ancestor, and list
      // items require a parent list (must be direct DOM parent).
      RemoveSubtreeWithFlatTraversal(node, /* remove_root */ true,
                                     /* notify_parent */ true);
    } else {
      // The children of this thing need to detach from parent.
      Remove(obj, /* notify_parent */ true);
    }
    // The aria-owns relation may have changed if the role changed,
    // because some roles allow aria-owns and others don't.
    // In addition, any owned objects need to reset their parent_ to point
    // to the new object.
    if (AXObject* new_object = GetOrCreate(node)) {
      relation_cache_->UpdateAriaOwnsWithCleanLayout(new_object, true);
      // Notify parent synchronously (Remove() does it async).
      DCHECK(new_object->CachedParentObject());
      ChildrenChangedWithCleanLayout(new_object->CachedParentObject());
    }
  }
}

void AXObjectCacheImpl::HandleAttributeChanged(const QualifiedName& attr_name,
                                               Element* element) {
  DCHECK(element);
  if (attr_name.LocalName().StartsWith("aria-")) {
    // Perform updates specific to each attribute.
    if (attr_name == html_names::kAriaActivedescendantAttr) {
      DeferTreeUpdate(TreeUpdateReason::kActiveDescendantChanged, element);
    } else if (attr_name == html_names::kAriaValuenowAttr ||
               attr_name == html_names::kAriaValuetextAttr) {
      HandleValueChanged(element);
    } else if (attr_name == html_names::kAriaLabelAttr ||
               attr_name == html_names::kAriaLabeledbyAttr ||
               attr_name == html_names::kAriaLabelledbyAttr) {
      DeferTreeUpdate(
          TreeUpdateReason::kSectionOrRegionRoleMaybeChangedFromLabel, element);
    } else if (attr_name == html_names::kAriaDescriptionAttr ||
               attr_name == html_names::kAriaDescribedbyAttr) {
      TextChanged(element);
    } else if (attr_name == html_names::kAriaCheckedAttr) {
      PostNotification(element, ax::mojom::blink::Event::kCheckedStateChanged);
    } else if (attr_name == html_names::kAriaPressedAttr) {
      DeferTreeUpdate(TreeUpdateReason::kAriaPressedChanged, element);
    } else if (attr_name == html_names::kAriaSelectedAttr) {
      DeferTreeUpdate(TreeUpdateReason::kAriaSelectedChanged, element);
    } else if (attr_name == html_names::kAriaExpandedAttr) {
      DeferTreeUpdate(TreeUpdateReason::kAriaExpandedChanged, element);
    } else if (attr_name == html_names::kAriaHiddenAttr) {
      DeferTreeUpdate(TreeUpdateReason::kInvalidateCachedValuesOnSubtree,
                      element);
    } else if (attr_name == html_names::kAriaOwnsAttr) {
      DeferTreeUpdate(TreeUpdateReason::kAriaOwnsChanged, element);
    } else if (attr_name == html_names::kAriaHaspopupAttr) {
      if (AXObject* obj = Get(element)) {
        if (obj->RoleValue() == ax::mojom::blink::Role::kButton ||
            obj->RoleValue() == ax::mojom::blink::Role::kPopUpButton) {
          // The aria-haspopup attribute can switch the role between kButton and
          // kPopupButton.
          DeferTreeUpdate(TreeUpdateReason::kRoleChangeFromAriaHasPopup,
                          element);
        }
      }
    } else if (attr_name == html_names::kAriaControlsAttr ||
               attr_name == html_names::kAriaDetailsAttr ||
               attr_name == html_names::kAriaErrormessageAttr ||
               attr_name == html_names::kAriaFlowtoAttr) {
      MarkElementDirty(element);
      if (AXObject* obj = SafeGet(element)) {
        relation_cache_->RegisterIncompleteRelation(obj, attr_name);
      }
    } else {
      MarkElementDirty(element);
    }
    return;
  }

  if (attr_name == html_names::kRoleAttr ||
      attr_name == html_names::kTypeAttr) {
    DeferTreeUpdate(TreeUpdateReason::kRoleChangeFromRoleOrType, element);
  } else if (attr_name == html_names::kSizeAttr ||
             attr_name == html_names::kMultipleAttr) {
    if (IsA<HTMLSelectElement>(element)) {
      // <select> size or multiple attribute changes can cause major structural
      // changes that we don't get good notifications for, because the popup
      // object can be an AXMenuListPopup, which is a mock object that has no
      // DOM node or layout object backing. The simplest thing in this case is
      // to just wipe the subtree and start over.
      RemoveSubtreeWhenSafe(element);
    }
  } else if (attr_name == html_names::kAltAttr) {
    TextChanged(element);
  } else if (attr_name == html_names::kTitleAttr) {
    DeferTreeUpdate(TreeUpdateReason::kSectionOrRegionRoleMaybeChangedFromTitle,
                    element);
  } else if (attr_name == html_names::kForAttr &&
             IsA<HTMLLabelElement>(*element)) {
    DeferTreeUpdate(TreeUpdateReason::kLabelChanged, element);
  } else if (attr_name == html_names::kIdAttr) {
    DeferTreeUpdate(TreeUpdateReason::kIdChanged, element);
  } else if (attr_name == html_names::kTabindexAttr) {
    DeferTreeUpdate(TreeUpdateReason::kFocusableChanged, element);
  } else if (attr_name == html_names::kValueAttr) {
    HandleValueChanged(element);
  } else if (attr_name == html_names::kDisabledAttr ||
             attr_name == html_names::kReadonlyAttr ||
             attr_name == html_names::kMinAttr ||
             attr_name == html_names::kMaxAttr ||
             attr_name == html_names::kStepAttr) {
    MarkElementDirty(element);
  } else if (attr_name == html_names::kUsemapAttr) {
    DeferTreeUpdate(TreeUpdateReason::kUseMapAttributeChanged, element);
  } else if (attr_name == html_names::kNameAttr) {
    DeferTreeUpdate(TreeUpdateReason::kNameAttributeChanged, element);
  } else if (attr_name == html_names::kControlsAttr) {
    ChildrenChanged(element);
  } else if (attr_name == html_names::kHrefAttr) {
    DeferTreeUpdate(TreeUpdateReason::kRoleMaybeChangedFromHref, element);
  }
}

void AXObjectCacheImpl::HandleUseMapAttributeChangedWithCleanLayout(
    Node* node) {
  if (!IsA<HTMLImageElement>(node)) {
    return;
  }
  // Get an area (aka image link) from the previous usemap.
  AXObject* ax_image = Get(node);
  AXObject* ax_image_link =
      ax_image ? ax_image->FirstChildIncludingIgnored() : nullptr;
  HTMLMapElement* previous_map =
      ax_image_link && ax_image_link->GetNode()
          ? Traversal<HTMLMapElement>::FirstAncestor(*ax_image_link->GetNode())
          : nullptr;
  // Both the old and new image may change image <--> image map.
  HandleRoleChangeWithCleanLayout(node);
  if (previous_map)
    HandleRoleChangeWithCleanLayout(previous_map->ImageElement());
}

void AXObjectCacheImpl::HandleNameAttributeChangedWithCleanLayout(Node* node) {
  // Changing a map name can alter an image's role and children.
  // The name has already changed, so we can no longer find the primary image
  // via the DOM. Use an area child's parent to find the old image.
  // If the old image was treated as a map, and now isn't, it will take care
  // of updating any other image that is newly associated with the map,
  // via AXNodeObject::AddImageMapChildren().
  if (HTMLMapElement* map = DynamicTo<HTMLMapElement>(node)) {
    if (AXObject* ax_previous_image = GetAXImageForMap(*map))
      HandleRoleChangeWithCleanLayout(ax_previous_image->GetNode());
  }
}

AXObject* AXObjectCacheImpl::GetOrCreateValidationMessageObject() {
  AXObject* message_ax_object = nullptr;
  // Create only if it does not already exist.
  if (validation_message_axid_) {
    message_ax_object = ObjectFromAXID(validation_message_axid_);
  }
  if (message_ax_object) {
    DCHECK(!message_ax_object->IsDetached());
    if (message_ax_object->IsMissingParent()) {
      message_ax_object->SetParent(Root());  // Reattach to parent (root).
    } else {
      DCHECK(message_ax_object->CachedParentObject() == Root());
    }
  } else {
    message_ax_object = MakeGarbageCollected<AXValidationMessage>(*this);
    DCHECK(message_ax_object);
    // Cache the validation message container for reuse.
    validation_message_axid_ = AssociateAXID(message_ax_object);
    // Validation message alert object is a child of the document, as not all
    // form controls can have a child. Also, there are form controls such as
    // listbox that technically can have children, but they are probably not
    // expected to have alerts within AT client code.
    message_ax_object->Init(Root());
  }
  return message_ax_object;
}

AXObject* AXObjectCacheImpl::ValidationMessageObjectIfInvalid(
    bool notify_children_changed) {
  Element* focused_element = document_->FocusedElement();
  if (focused_element) {
    ListedElement* form_control = ListedElement::From(*focused_element);
    if (form_control && !form_control->IsNotCandidateOrValid()) {
      // These must both be true:
      // * Focused control is currently invalid.
      // * Validation message was previously created but hidden
      // from timeout or currently visible.
      bool was_validation_message_already_created = validation_message_axid_;
      if (was_validation_message_already_created ||
          form_control->IsValidationMessageVisible()) {
        AXObject* focused_object = FocusedObject();
        if (focused_object) {
          // Return as long as the focused form control isn't overriding with a
          // different message via aria-errormessage.
          AXObject::AXObjectVector aria_error_messages =
              focused_object->ErrorMessageFromAria();
          if (aria_error_messages.empty()) {
            AXObject* message = GetOrCreateValidationMessageObject();
            DCHECK(message);
            DCHECK(!message->IsDetached());
            if (notify_children_changed &&
                Root()->FirstChildIncludingIgnored() != message) {
              // Only notify children changed if not already processing new root
              // children, and the root doesn't already have this child.
              ChildrenChanged(document_);
            }
            DCHECK_EQ(message->CachedParentObject(), Root());
            return message;
          }
        }
      }
    }
  }

  // No focused, invalid form control.
  if (validation_message_axid_) {
    DeferTreeUpdate(
        TreeUpdateReason::
            kRemoveValidationMessageObjectFromValidationMessageObject,
        document_);
  }
  return nullptr;
}

void AXObjectCacheImpl::RemoveValidationMessageObjectWithCleanLayout(
    Node* document) {
  DCHECK_EQ(document, document_);
  if (validation_message_axid_) {
    // Remove when it becomes hidden, so that a new object is created the next
    // time the message becomes visible. It's not possible to reuse the same
    // alert, because the event generator will not generate an alert event if
    // the same object is hidden and made visible quickly, which occurs if the
    // user submits the form when an alert is already visible.
    Remove(validation_message_axid_, /* notify_parent */ true);
    validation_message_axid_ = 0;
  }
}

// Native validation error popup for focused form control in current document.
void AXObjectCacheImpl::HandleValidationMessageVisibilityChanged(
    Node* form_control) {
  DCHECK(form_control);
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  DeferTreeUpdate(TreeUpdateReason::kValidationMessageVisibilityChanged,
                  form_control);
}

void AXObjectCacheImpl::HandleValidationMessageVisibilityChangedWithCleanLayout(
    const Node* form_control) {
#if DCHECK_IS_ON()
  DCHECK(form_control);
  Document* document = &form_control->GetDocument();
  DCHECK(document);
  DCHECK(document->Lifecycle().GetState() >= DocumentLifecycle::kLayoutClean)
      << "Unclean document at lifecycle " << document->Lifecycle().ToString();
#endif  // DCHECK_IS_ON()

  AXObject* message_ax_object = ValidationMessageObjectIfInvalid(
      /* Fire children changed on root if it gains message child */ true);
  if (message_ax_object)  // May be invisible now.
    MarkAXObjectDirtyWithCleanLayout(message_ax_object);

  // If the form control is invalid, it will now have an error message relation
  // to the message container.
  MarkElementDirtyWithCleanLayout(form_control);
}

void AXObjectCacheImpl::HandleEventListenerAdded(
    Node& node,
    const AtomicString& event_type) {
  // If this is the first |event_type| listener for |node|, handle the
  // subscription change.
  if (node.NumberOfEventListeners(event_type) == 1)
    HandleEventSubscriptionChanged(node, event_type);
}

void AXObjectCacheImpl::HandleEventListenerRemoved(
    Node& node,
    const AtomicString& event_type) {
  // If there are no more |event_type| listeners for |node|, handle the
  // subscription change.
  if (node.NumberOfEventListeners(event_type) == 0)
    HandleEventSubscriptionChanged(node, event_type);
}

bool AXObjectCacheImpl::DoesEventListenerImpactIgnoredState(
    const AtomicString& event_type,
    const Node& node) const {
  // An SVG graphics element with a focus event listener is focusable, which
  // causes it to be unignored.
  if (auto* svg_graphics_element = DynamicTo<SVGGraphicsElement>(node)) {
    if (svg_graphics_element->HasFocusEventListeners()) {
      return true;
    }
  }
  // A mouse event listener causes a node to be unignored.
  return event_util::IsMouseButtonEventType(event_type);
}

void AXObjectCacheImpl::HandleEventSubscriptionChanged(
    Node& node,
    const AtomicString& event_type) {
  // Adding or Removing an event listener for certain events may affect whether
  // a node or its descendants should be accessibility ignored.
  if (!DoesEventListenerImpactIgnoredState(event_type, node)) {
    return;
  }

  MarkElementDirty(&node);
  // If the ignored state changes, the parent's children may have changed.
  if (AXObject* obj = SafeGet(&node)) {
    if (!obj->IsDetached()) {
      if (obj->CachedParentObject()) {
        ChildrenChanged(obj->CachedParentObject());
        // ChildrenChanged() can cause the obj to be detached.
        if (obj->IsDetached()) {
          return;
        }
      }

      // The role of an element depends on whether it has an event listener, so
      // check if the role changed, and if so re-create the object.
      if (obj->RoleValue() != obj->DetermineAccessibilityRole()) {
        DeferTreeUpdate(TreeUpdateReason::kRoleMaybeChangedFromEventListener,
                        &node);
      }
    }
  }
}

void AXObjectCacheImpl::LabelChangedWithCleanLayout(Node* node) {
  // Will call back to TextChanged() when done updating relation cache.
  relation_cache_->LabelChanged(To<Element>(node));
}

void AXObjectCacheImpl::IdChangedWithCleanLayout(Node* node) {
  if (AXObject* obj = Get(node)) {
    // The id attribute has changed, which can change an object's ignored
    // state, because an object backed with an element having an id attribute
    // is always unignored, since it could be the end point of a relation.
    // Call UpdateCachedAttributeValuesIfNeeded() to force the ignored state
    // and included states to be recomputed, and if it tree inclusion changes,
    // this call will also recompute the tree structure.
    // TODO(aleventhal) This should no longer be necessary, because queuing this
    // method via DefertreeUpdate() should have already marked the node dirty,
    // and any next call for an cached value will call
    // UpdateCachedAttributeValuesIfNeeded().
    obj->UpdateCachedAttributeValuesIfNeeded();
    // When the id attribute changes, the relations its in may also change.
    MaybeNewRelationTarget(*node, obj);
  }
}

void AXObjectCacheImpl::AriaOwnsChangedWithCleanLayout(Node* node) {
  if (AXObject* obj = GetOrCreate(node)) {
    relation_cache_->UpdateAriaOwnsWithCleanLayout(obj);
  }
}

void AXObjectCacheImpl::InlineTextBoxesUpdated(LayoutObject* layout_object) {
  if (!InlineTextBoxAccessibilityEnabled())
    return;

  auto it = layout_object_mapping_.find(layout_object);
  AXID ax_id = it != layout_object_mapping_.end() ? it->value : 0;
  DCHECK(!WTF::IsHashTraitsDeletedValue<HashTraits<AXID>>(ax_id));

  // Only update if the accessibility object already exists and it's
  // not already marked as dirty.
  // Do not use Get(): it does extra work to determine whether the object should
  // be invalidated, including calling IsLayoutObjectRelevantForAccessibility(),
  // which uses the NGInlineCursor. However, the NGInlineCursor cannot be used
  // while inline boxes are being updated.
  if (ax_id) {
    AXObject* obj = objects_.at(ax_id);
    DCHECK(obj);
    DCHECK(obj->IsAXLayoutObject());
    DCHECK(!obj->IsDetached());
    if (!obj->NeedsToUpdateChildren()) {
      obj->SetNeedsToUpdateChildren();
      MarkAXObjectDirty(obj);
    }
  }
}

Settings* AXObjectCacheImpl::GetSettings() {
  return document_->GetSettings();
}

bool AXObjectCacheImpl::InlineTextBoxAccessibilityEnabled() {
  Settings* settings = GetSettings();
  if (!settings)
    return false;
  return settings->GetInlineTextBoxAccessibilityEnabled();
}

const Element* AXObjectCacheImpl::RootAXEditableElement(const Node* node) {
  const Element* result = RootEditableElement(*node);
  const auto* element = DynamicTo<Element>(node);
  if (!element)
    element = node->parentElement();

  for (; element; element = element->parentElement()) {
    if (NodeIsTextControl(element))
      result = element;
  }

  return result;
}

bool AXObjectCacheImpl::NodeIsTextControl(const Node* node) {
  if (!node)
    return false;

  const AXObject* ax_object = GetOrCreate(const_cast<Node*>(node));
  return ax_object && ax_object->IsTextField();
}

bool IsNodeAriaVisible(Node* node) {
  auto* element = DynamicTo<Element>(node);
  if (!element)
    return false;

  bool is_null = true;
  bool hidden = AccessibleNode::GetPropertyOrARIAAttribute(
      element, AOMBooleanProperty::kHidden, is_null);
  return !is_null && !hidden;
}

WebLocalFrameClient* AXObjectCacheImpl::GetWebLocalFrameClient() const {
  DCHECK(document_);
  WebLocalFrameImpl* web_frame =
      WebLocalFrameImpl::FromFrame(document_->AXObjectCacheOwner().GetFrame());
  if (!web_frame)
    return nullptr;
  WebLocalFrameClient* client = web_frame->Client();
  DCHECK(client);
  return client;
}

void AXObjectCacheImpl::PostPlatformNotification(
    AXObject* obj,
    ax::mojom::blink::Event event_type,
    ax::mojom::blink::EventFrom event_from,
    ax::mojom::blink::Action event_from_action,
    const BlinkAXEventIntentsSet& event_intents) {
  obj = GetSerializationTarget(obj);
  if (!obj)
    return;

  ui::AXEvent event;
  event.id = obj->AXObjectID();
  event.event_type = event_type;
  event.event_from = event_from;
  event.event_from_action = event_from_action;
  event.event_intents.resize(event_intents.size());
  // We need to filter out the counts from every intent.
  base::ranges::transform(
      event_intents, event.event_intents.begin(),
      [](const auto& intent) { return intent.key.intent(); });
  for (auto agent : agents_)
    agent->AXEventFired(obj, event_type);

  if (auto* client = GetWebLocalFrameClient()) {
    // TODO(accessibility) This doesn't need to call into RAI -- it
    // can add to pending events and dirty objects here. The only reason to call
    // into RAI would be during a page load, to inform in the case of an
    // event that requires immediate serialization, such as focus.
    // MarkAXObjectDirtyWithDetails(obj, false, event_from, event_from_action,
    //                              event.event_intents);
    // AddPendingEvent(event);
    client->PostAccessibilityEvent(event);
  }
}

void AXObjectCacheImpl::EnsureMarkDirtyWithCleanLayout(Node* node) {
  MarkAXObjectDirtyWithCleanLayout(GetOrCreate(node));
}

void AXObjectCacheImpl::MarkAXObjectDirtyWithCleanLayoutHelper(
    AXObject* obj,
    bool subtree,
    ax::mojom::blink::EventFrom event_from,
    ax::mojom::blink::Action event_from_action) {
  obj = GetSerializationTarget(obj);
  if (!obj)
    return;

  // TODO(chrishtr): handle |subtree|, or remove subtree as an option, as it
  // isn't used very often and there are other possibilities.
  obj->SetAncestorsHaveDirtyDescendants();

  // If the content is inside the popup, mark the owning element dirty.
  // TODO(aleventhal): not sure why this works, but now that we run a11y in
  // PostRunLifecycleTasks(), we need this, otherwise the pending updates in
  // the popup aren't processed.
  if (IsPopup(*obj->GetDocument())) {
    MarkElementDirtyWithCleanLayout(GetDocument().FocusedElement());
  }

  // TODO(aleventhal) This is for web tests only, in order to record MarkDirty
  // events. Is there a way to avoid these calls for normal browsing?
  // Maybe we should use dependency injection from AccessibilityController.
  if (auto* client = GetWebLocalFrameClient())
    client->NotifyWebAXObjectMarkedDirty(WebAXObject(obj));

  std::vector<ui::AXEventIntent> event_intents;
  MarkAXObjectDirtyWithDetails(obj, subtree, event_from, event_from_action,
                               event_intents);

  obj->UpdateCachedAttributeValuesIfNeeded(true);
  for (auto agent : agents_)
    agent->AXObjectModified(obj, subtree);
}

void AXObjectCacheImpl::MarkAXObjectDirtyWithCleanLayoutAndEvent(
    AXObject* obj,
    ax::mojom::blink::EventFrom event_from,
    ax::mojom::blink::Action event_from_action) {
  MarkAXObjectDirtyWithCleanLayoutHelper(obj, false, event_from,
                                         event_from_action);
}

void AXObjectCacheImpl::MarkAXObjectDirtyWithCleanLayout(AXObject* obj) {
  MarkAXObjectDirtyWithCleanLayoutHelper(obj, false, active_event_from_,
                                         active_event_from_action_);
}

void AXObjectCacheImpl::MarkAXSubtreeDirtyWithCleanLayout(AXObject* obj) {
  MarkAXObjectDirtyWithCleanLayoutHelper(obj, true, active_event_from_,
                                         active_event_from_action_);
}

void AXObjectCacheImpl::MarkAXObjectDirty(AXObject* obj) {
  if (!obj)
    return;

  // TODO(accessibility) Consider catching all redundant dirty object work,
  // perhaps by setting a flag on the AXObject, or by adding the id to a set of
  // already-dirtied objects.
  DeferTreeUpdate(TreeUpdateReason::kMarkAXObjectDirty, obj);
}

void AXObjectCacheImpl::MarkAXSubtreeDirty(AXObject* obj) {
  if (!obj)
    return;

  DeferTreeUpdate(TreeUpdateReason::kMarkAXSubtreeDirty, obj);
}

void AXObjectCacheImpl::MarkDocumentDirty() {
  mark_all_dirty_ = true;
  // Assume all nodes in the tree need to recompute their properties.
  // Note that objects can remain in the tree without being re-created.
  // However, they will be dropped if they are no longer needed as the tree
  // structure is rebuilt from the top down.
  for (auto& entry : objects_) {
    AXObject* object = entry.value;
    DCHECK(!object->IsDetached());
    object->InvalidateCachedValues();
  }

  ScheduleAXUpdate();
}

void AXObjectCacheImpl::MarkDocumentDirtyWithCleanLayout() {
  // This function will cause everything to be reserialized from the root down,
  // but will not create new AXObjects, which avoids resetting the user's
  // position in the content.
  DCHECK(mark_all_dirty_);
  mark_all_dirty_ = false;

  // Don't keep previous parent-child relationships.
  // This loop operates on a copy of values in the objects_ map, because some
  // entries may be removed from objects_ while iterating.
  HeapVector<Member<AXObject>> objects;
  CopyValuesToVector(objects_, objects);
  for (auto& object : objects) {
    if (!object->IsDetached()) {
      object->SetNeedsToUpdateChildren();
    }
  }

  // Clear anything about to be serialized, because everything will be
  // reserialized anyway.
  dirty_objects_.clear();

  // Tell the serializer that everything will need to be serialized.
  DCHECK(Root());
  Root()->SetHasDirtyDescendants(true);
  MarkAXSubtreeDirtyWithCleanLayout(Root());
  ChildrenChangedWithCleanLayout(Root());
}

void AXObjectCacheImpl::ResetSerializer() {
  ax_tree_serializer_->Reset();

  // Clear anything about to be serialized, because everything will be
  // reserialized anyway.
  dirty_objects_.clear();
  pending_events_.clear();

  // Send the serialization at the next available opportunity.
  ScheduleAXUpdate();
}

void AXObjectCacheImpl::MarkElementDirty(const Node* element) {
  // Warning, if no AXObject exists for element, nothing is marked dirty.
  MarkAXObjectDirty(Get(element));
}

WTF::Vector<TextChangedOperation>*
AXObjectCacheImpl::GetFromTextOperationInNodeIdMap(AXID id) {
  auto it = text_operation_in_node_ids_.find(id);
  if (it != text_operation_in_node_ids_.end()) {
    return &it.Get()->value;
  }
  return nullptr;
}

void AXObjectCacheImpl::ClearTextOperationInNodeIdMap() {
  text_operation_in_node_ids_.clear();
}

void AXObjectCacheImpl::MarkElementDirtyWithCleanLayout(const Node* element) {
  // Warning, if no AXObject exists for element, nothing is marked dirty.
  MarkAXObjectDirtyWithCleanLayout(Get(element));
}

AXObject* AXObjectCacheImpl::GetSerializationTarget(AXObject* obj) {
  if (!obj || obj->IsDetached() || !obj->GetDocument() ||
      !obj->GetDocument()->View() ||
      !obj->GetDocument()->View()->GetFrame().GetPage()) {
    return nullptr;
  }

  // A <slot> descendant of a node that is still in the DOM but no longer
  // rendered will return true for Node::isConnected() and false for
  // AXObject::IsDetached(). But from the perspective of platform ATs, this
  // subtree is not connected and is detached.
  // TODO(accessibility): The relevance check probably applies to all nodes
  // not just slot elements.
  if (const HTMLSlotElement* slot =
          ToHTMLSlotElementIfSupportsAssignmentOrNull(obj->GetNode())) {
    if (!AXObjectCacheImpl::IsRelevantSlotElement(*slot))
      return nullptr;
  }

  // Ensure still in tree.
  if (obj->IsMissingParent()) {
    // TODO(accessibility) Only needed because of <select> size changes.
    // This should become a DCHECK(!obj->IsMissingParent()) once the shadow DOM
    // is used for <select> elements instead of AXMenuList* and AXListBox*
    // classes.
    if (!RestoreParentOrPrune(obj))
      return nullptr;
  }

  // Return included in tree object.
  if (obj->AccessibilityIsIncludedInTree())
    return obj;

  return obj->ParentObjectIncludedInTree();
}

AXObject* AXObjectCacheImpl::RestoreParentOrPrune(AXObject* child) {
  AXObject* parent = child->ComputeParentOrNull();
  if (parent) {
    child->SetParent(parent);
  } else {
    // If no parent is possible, the child is no longer part of the tree.
    RemoveSubtreeWhenSafe(child->GetNode());
  }

  return parent;
}

void AXObjectCacheImpl::HandleFocusedUIElementChanged(
    Element* old_focused_element,
    Element* new_focused_element) {
  TRACE_EVENT0("accessibility",
               "AXObjectCacheImpl::HandleFocusedUIElementChanged");
  Document& focused_doc =
      new_focused_element ? new_focused_element->GetDocument() : *document_;

#if DCHECK_IS_ON()
  // The focus can be in a different document when a popup is open.
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();
#endif  // DCHECK_IS_ON()

  if (focused_doc.GetPage() && focused_doc.GetPage()->InsidePortal())
    return;  // Elements inside a portal are not considered focusable.

  if (validation_message_axid_) {
    DeferTreeUpdate(
        TreeUpdateReason::kRemoveValidationMessageObjectFromFocusedUIElement,
        document_);
  }

  if (!new_focused_element) {
    // When focus is cleared, implicitly focus the document by sending a blur.
    if (GetDocument().documentElement()) {
      DeferTreeUpdate(TreeUpdateReason::kNodeLostFocus,
                      GetDocument().documentElement());
    }
    return;
  }

  Page* page = new_focused_element->GetDocument().GetPage();
  if (!page)
    return;

  if (old_focused_element) {
    DeferTreeUpdate(TreeUpdateReason::kNodeLostFocus, old_focused_element);
  }

  Settings* settings = GetSettings();
  if (settings && settings->GetAriaModalPrunesAXTree())
    UpdateActiveAriaModalDialog(new_focused_element);

  DeferTreeUpdate(TreeUpdateReason::kNodeGainedFocus, FocusedElement());
}

// Check if the focused node is inside an active aria-modal dialog. If so, we
// should mark the cache as dirty to recompute the ignored status of each node.
void AXObjectCacheImpl::UpdateActiveAriaModalDialog(Node* node) {
  AXObject* new_active_aria_modal = AncestorAriaModalDialog(node);
  if (active_aria_modal_dialog_ == new_active_aria_modal)
    return;

  active_aria_modal_dialog_ = new_active_aria_modal;
  MarkDocumentDirty();
}

AXObject* AXObjectCacheImpl::AncestorAriaModalDialog(Node* node) {
  for (Element* ancestor = Traversal<Element>::FirstAncestorOrSelf(*node);
       ancestor; ancestor = Traversal<Element>::FirstAncestor(*ancestor)) {
    if (!ancestor->FastHasAttribute(html_names::kAriaModalAttr))
      continue;

    AtomicString aria_modal =
        ancestor->FastGetAttribute(html_names::kAriaModalAttr);
    if (!EqualIgnoringASCIICase(aria_modal, "true")) {
      continue;
    }

    AXObject* ancestor_ax_object = GetOrCreate(ancestor);
    if (!ancestor_ax_object)
      return nullptr;
    ax::mojom::blink::Role ancestor_role = ancestor_ax_object->RoleValue();

    if (!ui::IsDialog(ancestor_role))
      continue;

    return ancestor_ax_object;
  }
  return nullptr;
}

AXObject* AXObjectCacheImpl::GetActiveAriaModalDialog() const {
  return active_aria_modal_dialog_;
}

void AXObjectCacheImpl::SerializeLocationChanges() {
  if (changed_bounds_ids_.empty())
    return;
  Vector<mojom::blink::LocationChangesPtr> changes;
  changes.reserve(changed_bounds_ids_.size());
  for (AXID changed_bounds_id : changed_bounds_ids_) {
    if (AXObject* obj = ObjectFromAXID(changed_bounds_id)) {
      DCHECK(!obj->IsDetached());
      // Only update locations that are already known.
      auto bounds = cached_bounding_boxes_.find(changed_bounds_id);
      if (bounds == cached_bounding_boxes_.end())
        continue;

      ui::AXRelativeBounds new_location;
      bool clips_children;
      obj->PopulateAXRelativeBounds(new_location, &clips_children);
      if (bounds->value == new_location)
        continue;

      cached_bounding_boxes_.Set(changed_bounds_id, new_location);
      changes.push_back(
          mojom::blink::LocationChanges::New(changed_bounds_id, new_location));
    }
  }
  changed_bounds_ids_.clear();
  if (!changes.empty()) {
    GetOrCreateRemoteRenderAccessibilityHost()->HandleAXLocationChanges(
        std::move(changes));
  }
}

bool AXObjectCacheImpl::SerializeEntireTree(size_t max_node_count,
                                            base::TimeDelta timeout,
                                            ui::AXTreeUpdate* response) {
  BlinkAXTreeSource* tree_source = BlinkAXTreeSource::Create(*this);

  // The serializer returns an ui::AXTreeUpdate, which can store a complete
  // or a partial accessibility tree. AXTreeSerializer is stateful, but the
  // first time you serialize from a brand-new tree you're guaranteed to get a
  // complete tree.
  ui::AXTreeSerializer<AXObject*> serializer(tree_source);

  if (max_node_count)
    serializer.set_max_node_count(max_node_count);
  if (!timeout.is_zero())
    serializer.set_timeout(timeout);

  tree_source->Freeze();

  if (!tree_source->GetRoot() || tree_source->GetRoot()->IsDetached()) {
    // TODO(chrishtr): not clear why this can happen.
    DCHECK(tree_source->GetRoot());
    DCHECK(!tree_source->GetRoot()->IsDetached())
        << tree_source->GetRoot()->ToString(true);
    tree_source->Thaw();
    return false;
  }

  bool success = serializer.SerializeChanges(tree_source->GetRoot(), response);
  DCHECK(success)
      << "Serializer failed. Should have hit DCHECK inside of serializer.";

  tree_source->Thaw();
  return true;
}

void AXObjectCacheImpl::MarkAXObjectDirtyWithDetails(
    AXObject* obj,
    bool subtree,
    ax::mojom::blink::EventFrom event_from,
    ax::mojom::blink::Action event_from_action,
    const std::vector<ui::AXEventIntent>& event_intents) {
  dirty_objects_.push_back(
      AXDirtyObject::Create(obj, event_from, event_from_action, event_intents));

  if (subtree)
    MarkSerializerSubtreeDirty(*obj);
}

void AXObjectCacheImpl::SerializeDirtyObjectsAndEvents(
    bool has_plugin_tree_source,
    std::vector<ui::AXTreeUpdate>& updates,
    std::vector<ui::AXEvent>& events,
    bool& had_end_of_test_event,
    bool& had_load_complete_messages,
    bool& need_to_send_location_changes) {
  // Make a copy of the events, because it's possible that
  // actions inside this loop will cause more events to be
  // queued up.
  Deque<ui::AXEvent> src_events = pending_events_;
  pending_events_.clear();

  // Dirty objects can be added as a result of serialization. For example,
  // as children are iterated during depth first traversal in the serializer,
  // the children sometimes need to be created. The initialization of these
  // new children can lead to the discovery of parenting changes via
  // aria-owns, or name changes on an ancestor that collects its name its from
  // contents. In some cases this has led to an infinite loop, as the
  // serialization of new dirty objects keeps adding new dirty objects to
  // consider. The infinite loop is avoided by tracking the number of dirty
  // objects that can be serialized from the loop, which is the initial
  // number of dirty objects + kMaxExtraDirtyObjectsToSerialize.
  // Allowing kMaxExtraDirtyObjectsToSerialize ensures that most important
  // additional related changes occur at the same time, and that dump event
  // tests have consistent results (the results change when dirty objects are
  // processed in separate batches).
  constexpr int kMaxExtraDirtyObjectsToSerialize = 100;

  size_t num_remaining_objects_to_serialize =
      dirty_objects_.size() + kMaxExtraDirtyObjectsToSerialize;

  HashSet<int32_t> already_serialized_ids;
  int redundant_serialization_count = 0;

  DCHECK_GE(GetDocument().Lifecycle().GetState(),
            DocumentLifecycle::kLayoutClean);
  DCHECK(!popup_document_ || popup_document_->Lifecycle().GetState() >=
                                 DocumentLifecycle::kLayoutClean);

  while (!dirty_objects_.empty() && --num_remaining_objects_to_serialize > 0) {
    AXDirtyObject* current_dirty_object = std::move(dirty_objects_.front());
    dirty_objects_.pop_front();
    AXObject* obj = current_dirty_object->obj;

    // Dirty objects can be added using MarkWebAXObjectDirty(obj) from other
    // parts of the code as well, so we need to ensure the object still
    // exists.
    if (!obj || obj->IsDetached()) {
      continue;
    }

    DCHECK(obj->GetDocument()->GetFrame())
        << "An object in a closed document should have been detached via "
           "Remove(): "
        << obj->ToString(true, true);

    // Cannot serialize unincluded object.
    // Only included objects are marked dirty, but this can happen if the
    // object becomes unincluded after it was originally marked dirty, in which
    // cas a children changed will also be fired on the included ancestor. The
    // children changed event on the ancestor means that attempting to
    // serialize this unincluded object is not necessary.
    if (!obj->AccessibilityIsIncludedInTree())
      continue;

    DCHECK(obj->AXObjectID());

    if (already_serialized_ids.Contains(obj->AXObjectID()))
      continue;  // No need to serialize, was already present.

    ui::AXTreeUpdate update;
    update.event_from = current_dirty_object->event_from;
    update.event_from_action = current_dirty_object->event_from_action;
    update.event_intents = current_dirty_object->event_intents;

    // If there's a plugin, force the tree data to be generated in every
    // message so the plugin can merge its own tree data changes.
    if (has_plugin_tree_source)
      update.has_tree_data = true;

    bool success = ax_tree_serializer_->SerializeChanges(obj, &update);

    DCHECK(success);
    DCHECK_GT(update.nodes.size(), 0U);

    for (auto& node_data : update.nodes) {
      DCHECK(node_data.id);
      auto result = already_serialized_ids.insert(node_data.id);
      if (!result.is_new_entry) {
        redundant_serialization_count++;
      }
    }

    DCHECK(already_serialized_ids.Contains(obj->AXObjectID()))
        << "Did not serialize original node, so it was probably not included "
           "in its parent's children, and should never have been marked dirty "
           "in the first place: "
        << obj->ToString(true)
        << "\nParent: " << obj->ParentObjectIncludedInTree()->ToString(true)
        << "\nIndex in parent: "
        << obj->ParentObjectIncludedInTree()
               ->CachedChildrenIncludingIgnored()
               .Find(obj);

    updates.push_back(update);
  }

  UMA_HISTOGRAM_COUNTS_10000(
      "Accessibility.Performance.AXObjectCacheImpl.RedundantSerializations",
      redundant_serialization_count);

  // Add kLayoutComplete if layout has changed.
  if (need_to_send_location_changes_) {
    need_to_send_location_changes_ = false;  // Class member is now clear.
    need_to_send_location_changes = true;    // Reference parameter.
    // TODO(accessibility) Remove the layout complete event, which is only
    // used by tests and as a signal to serialize location data.
    ui::AXEvent layout_complete_event(Root()->AXObjectID(),
                                      ax::mojom::blink::Event::kLayoutComplete);
    src_events.push_back(layout_complete_event);
  }

  // Loop over each event and generate an updated event message.
  for (ui::AXEvent& event : src_events) {
    if (event.event_type == ax::mojom::blink::Event::kEndOfTest) {
      had_end_of_test_event = true;
      continue;
    }

    if (!base::Contains(already_serialized_ids, event.id)) {
      // Node no longer exists or could not be serialized.
      VLOG(1) << "Dropped AXEvent: " << event.event_type << " on "
              << ObjectFromAXID(event.id);
      continue;
    }

#if DCHECK_IS_ON()
    AXObject* obj = ObjectFromAXID(event.id);
    DCHECK(obj && !obj->IsDetached())
        << "Detached object for AXEvent: " << event.event_type << " on #"
        << event.id;
#endif

    if (event.event_type == ax::mojom::blink::Event::kLoadComplete) {
      if (had_load_complete_messages)
        continue;  // De-dupe.
      had_load_complete_messages = true;
    }

    events.push_back(event);

    VLOG(1) << "AXEvent: " << event.event_type << " on "
            << ObjectFromAXID(event.id);
  }
}

void AXObjectCacheImpl::GetImagesToAnnotate(
    ui::AXTreeUpdate& update,
    std::vector<ui::AXNodeData*>& nodes) {
  for (auto& node : update.nodes) {
    AXObject* src = ObjectFromAXID(node.id);
    if (!src || src->IsDetached() || !src->AccessibilityIsIncludedInTree() ||
        (src->AccessibilityIsIgnored() &&
         !node.HasState(ax::mojom::blink::State::kFocusable))) {
      continue;
    }

    if (src->IsImage()) {
      nodes.push_back(&node);
      // This else clause matches links/documents because we would like to find
      // an image that is in the near-descendant subtree of the link/document,
      // since that image may be semantically representative of that
      // link/document. See FindExactlyOneInnerImageInMaxDepthThree (not in
      // this file), which is used by the caller of this method to find such
      // an image.
    } else if ((src->IsLink() || ui::IsPlatformDocument(node.role)) &&
               node.GetNameFrom() != ax::mojom::blink::NameFrom::kAttribute) {
      nodes.push_back(&node);
    }
  }
}

bool AXObjectCacheImpl::AddPendingEvent(const ui::AXEvent& event,
                                        bool insert_at_beginning) {
  if (insert_at_beginning)
    pending_events_.push_front(event);
  else
    pending_events_.push_back(event);
  return true;
}

HeapMojoRemote<blink::mojom::blink::RenderAccessibilityHost>&
AXObjectCacheImpl::GetOrCreateRemoteRenderAccessibilityHost() {
  if (!render_accessibility_host_) {
    GetDocument().GetFrame()->GetBrowserInterfaceBroker().GetInterface(
        render_accessibility_host_.BindNewPipeAndPassReceiver(
            document_->GetTaskRunner(TaskType::kUserInteraction)));
  }
  return render_accessibility_host_;
}

void AXObjectCacheImpl::HandleInitialFocus() {
  PostNotification(document_, ax::mojom::Event::kFocus);
}

void AXObjectCacheImpl::HandleEditableTextContentChanged(Node* node) {
  if (!node)
    return;

  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  DeferTreeUpdate(TreeUpdateReason::kEditableTextContentChanged, node);
}

void AXObjectCacheImpl::HandleDeletionOrInsertionInTextField(
    const SelectionInDOMTree& changed_selection,
    bool is_deletion) {
  Position start_pos = changed_selection.ComputeStartPosition();
  Position end_pos = changed_selection.ComputeEndPosition();

  // Currently there are scenarios where the start/end are not offset in
  // anchor, if this is the case, we need to compute their offset in the
  // container node since we need this information on the browser side.
  int start_offset = start_pos.ComputeOffsetInContainerNode();
  int end_offset = end_pos.ComputeOffsetInContainerNode();

  AXObject* start_obj = GetOrCreate(start_pos.ComputeContainerNode());
  AXObject* end_obj = GetOrCreate(end_pos.ComputeContainerNode());
  if (!start_obj || !end_obj) {
    return;
  }

  AXObject* text_field_obj = start_obj->GetTextFieldAncestor();
  if (!text_field_obj) {
    return;
  }

  auto it = text_operation_in_node_ids_.find(text_field_obj->AXObjectID());
  ax::mojom::blink::Command op = is_deletion
                                     ? ax::mojom::blink::Command::kDelete
                                     : ax::mojom::blink::Command::kInsert;
  if (it != text_operation_in_node_ids_.end()) {
    it->value.push_back(TextChangedOperation(start_offset, end_offset,
                                             start_obj->AXObjectID(),
                                             end_obj->AXObjectID(), op));
  } else {
    WTF::Vector<TextChangedOperation> info{
        TextChangedOperation(start_offset, end_offset, start_obj->AXObjectID(),
                             end_obj->AXObjectID(), op)};
    text_operation_in_node_ids_.Set(text_field_obj->AXObjectID(), info);
  }
}

void AXObjectCacheImpl::HandleEditableTextContentChangedWithCleanLayout(
    Node* node) {
  AXObject* obj = GetOrCreate(node);
  if (obj) {
    obj = obj->GetTextFieldAncestor();
  }

  PostNotification(obj, ax::mojom::Event::kValueChanged);
}

void AXObjectCacheImpl::HandleTextFormControlChanged(Node* node) {
  HandleEditableTextContentChanged(node);
}

void AXObjectCacheImpl::HandleTextMarkerDataAdded(Node* start, Node* end) {
  DCHECK(start);
  DCHECK(end);
  DCHECK(IsA<Text>(start));
  DCHECK(IsA<Text>(end));

  // Notify the client of new text marker data.
  // Ensure there is a delay so that the final marker state can be evaluated.
  DeferTreeUpdate(TreeUpdateReason::kTextMarkerDataAdded, start);
  if (start != end) {
    DeferTreeUpdate(TreeUpdateReason::kTextMarkerDataAdded, end);
  }
}

void AXObjectCacheImpl::HandleTextMarkerDataAddedWithCleanLayout(Node* node) {
  Text* text_node = To<Text>(node);
  // If non-spelling/grammar markers are present, assume that children changed
  // should be called.
  DocumentMarkerController& marker_controller = GetDocument().Markers();
  const DocumentMarker::MarkerTypes non_spelling_or_grammar_markers(
      DocumentMarker::kTextMatch | DocumentMarker::kActiveSuggestion |
      DocumentMarker::kSuggestion | DocumentMarker::kTextFragment |
      DocumentMarker::kCustomHighlight);
  if (!marker_controller.MarkersFor(*text_node, non_spelling_or_grammar_markers)
           .empty()) {
    ChildrenChangedWithCleanLayout(node);
    return;
  }

  // Spelling and grammar markers are removed and then readded in quick
  // succession. By checking these here (on a slight delay), we can determine
  // whether the presence of one of these markers actually changed, and only
  // fire ChildrenChangedWithCleanLayout() if they did.
  const DocumentMarker::MarkerTypes spelling_and_grammar_markers(
      DocumentMarker::DocumentMarker::kSpelling |
      DocumentMarker::DocumentMarker::kGrammar);
  bool has_spelling_or_grammar_markers =
      !marker_controller.MarkersFor(*text_node, spelling_and_grammar_markers)
           .empty();
  if (has_spelling_or_grammar_markers) {
    if (nodes_with_spelling_or_grammar_markers_.insert(node).is_new_entry)
      ChildrenChangedWithCleanLayout(node);
  } else {
    const auto& iter = nodes_with_spelling_or_grammar_markers_.find(node);
    if (iter != nodes_with_spelling_or_grammar_markers_.end()) {
      nodes_with_spelling_or_grammar_markers_.erase(iter);
      ChildrenChangedWithCleanLayout(node);
    }
  }
}

void AXObjectCacheImpl::HandleValueChanged(Node* node) {
  // Avoid duplicate processing of rapid value changes, e.g. on a slider being
  // dragged, or a progress meter.
  AXObject* ax_object = Get(node);
  if (ax_object) {
    if (last_value_change_node_ == ax_object->AXObjectID())
      return;
    last_value_change_node_ = ax_object->AXObjectID();
  }

  PostNotification(node, ax::mojom::Event::kValueChanged);

  // If it's a slider, invalidate the thumb's bounding box.
  if (ax_object && ax_object->RoleValue() == ax::mojom::blink::Role::kSlider &&
      !ax_object->NeedsToUpdateChildren() &&
      ax_object->ChildCountIncludingIgnored() == 1) {
    changed_bounds_ids_.insert(
        ax_object->ChildAtIncludingIgnored(0)->AXObjectID());
  }
}

void AXObjectCacheImpl::HandleUpdateActiveMenuOption(Node* menu_list) {
  if (!use_ax_menu_list_) {
    MarkElementDirty(menu_list);
    return;
  }

  DeferTreeUpdate(TreeUpdateReason::kUpdateActiveMenuOption, menu_list);
}

void AXObjectCacheImpl::HandleUpdateActiveMenuOptionWithCleanLayout(
    Node* menu_list) {
  if (AXMenuList* ax_menu_list = DynamicTo<AXMenuList>(GetOrCreate(menu_list)))
    ax_menu_list->DidUpdateActiveOption();
}

void AXObjectCacheImpl::DidShowMenuListPopup(LayoutObject* menu_list) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  DCHECK(menu_list->GetNode());
  DeferTreeUpdate(TreeUpdateReason::kDidShowMenuListPopup,
                  menu_list->GetNode());
}

void AXObjectCacheImpl::DidShowMenuListPopupWithCleanLayout(Node* menu_list) {
  if (!use_ax_menu_list_) {
    MarkAXObjectDirtyWithCleanLayout(Get(menu_list));
    return;
  }

  auto* ax_object = DynamicTo<AXMenuList>(Get(menu_list));
  if (ax_object)
    ax_object->DidShowPopup();
}

void AXObjectCacheImpl::DidHideMenuListPopup(LayoutObject* menu_list) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  DCHECK(menu_list->GetNode());
  DeferTreeUpdate(TreeUpdateReason::kDidHideMenuListPopup,
                  menu_list->GetNode());
}

void AXObjectCacheImpl::DidHideMenuListPopupWithCleanLayout(Node* menu_list) {
  if (!use_ax_menu_list_) {
    MarkAXObjectDirtyWithCleanLayout(Get(menu_list));
    return;
  }

  auto* ax_object = DynamicTo<AXMenuList>(Get(menu_list));
  if (ax_object)
    ax_object->DidHidePopup();
}

void AXObjectCacheImpl::HandleLoadStart(Document* document) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();
  // Popups do not need to fire load start or load complete , because ATs do not
  // regard popups as documents -- that is an implementation detail of the
  // browser. The AT regards popups as part of a widget, and a load start or
  // load complete event would only potentially confuse the AT.
  if (!IsPopup(*document) && !IsInitialEmptyDocument(*document)) {
    DeferTreeUpdate(TreeUpdateReason::kPostNotificationFromHandleLoadStart,
                    document, ax::mojom::blink::Event::kLoadStart);
  }
}

void AXObjectCacheImpl::HandleLoadComplete(Document* document) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  // TODO(accessibility) Change this to a DCHECK, but that would fail right now
  // in navigation API tests.
  if (!document->IsLoadCompleted())
    return;

  // Popups do not need to fire load start or load complete , because ATs do not
  // regard popups as documents -- that is an implementation detail of the
  // browser. The AT regards popups as part of a widget, and a load start or
  // load complete event would only potentially confuse the AT.
  if (!IsPopup(*document) && !IsInitialEmptyDocument(*document)) {
    AddPermissionStatusListener();
    DeferTreeUpdate(TreeUpdateReason::kPostNotificationFromHandleLoadComplete,
                    document, ax::mojom::blink::Event::kLoadComplete);
  }
}

void AXObjectCacheImpl::HandleLayoutComplete(Document* document) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();
  DCHECK(document);
  // Do not fire kLayoutComplete for popup document or initial empty document.
  if (IsPopup(*document) || IsInitialEmptyDocument(*document)) {
    return;
  }

  need_to_send_location_changes_ = true;
  MarkElementDirty(document);
  DeferTreeUpdate(TreeUpdateReason::kMarkDirtyFromHandleLayout, document);
}

void AXObjectCacheImpl::HandleScrolledToAnchor(const Node* anchor_node) {
  if (!anchor_node)
    return;

  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  AXObject* obj = GetOrCreate(anchor_node->GetLayoutObject());
  if (!obj)
    return;
  if (!obj->AccessibilityIsIncludedInTree())
    obj = obj->ParentObjectUnignored();
  PostNotification(obj, ax::mojom::Event::kScrolledToAnchor);
}

void AXObjectCacheImpl::HandleFrameRectsChanged(Document& document) {
  MarkElementDirty(&document);
}

void AXObjectCacheImpl::InvalidateBoundingBox(
    const LayoutObject* layout_object) {
  if (AXObject* obj = Get(const_cast<LayoutObject*>(layout_object))) {
    changed_bounds_ids_.insert(obj->AXObjectID());
  }
}

void AXObjectCacheImpl::SetCachedBoundingBox(
    AXID id,
    const ui::AXRelativeBounds& bounds) {
  cached_bounding_boxes_.Set(id, bounds);
}

void AXObjectCacheImpl::HandleScrollPositionChanged(
    LocalFrameView* frame_view) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  InvalidateBoundingBoxForFixedOrStickyPosition();
  need_to_send_location_changes_ = true;
  MarkElementDirty(document_);
}

void AXObjectCacheImpl::HandleScrollPositionChanged(
    LayoutObject* layout_object) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();
  InvalidateBoundingBoxForFixedOrStickyPosition();
  Node* node = GetClosestNodeForLayoutObject(layout_object);
  if (node) {
    need_to_send_location_changes_ = true;
    DeferTreeUpdate(TreeUpdateReason::kMarkDirtyFromHandleScroll, node);
  }
}

const AtomicString& AXObjectCacheImpl::ComputedRoleForNode(Node* node) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  AXObject* obj = GetOrCreate(node);
  if (!obj)
    return AXObject::ARIARoleName(ax::mojom::blink::Role::kUnknown);
  return AXObject::ARIARoleName(obj->RoleValue());
}

String AXObjectCacheImpl::ComputedNameForNode(Node* node) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();
  AXObject* obj = GetOrCreate(node);
  if (!obj)
    return "";

  return obj->ComputedName();
}

void AXObjectCacheImpl::OnTouchAccessibilityHover(const gfx::Point& location) {
  DocumentLifecycle::DisallowTransitionScope disallow(document_->Lifecycle());
  AXObject* hit = Root()->AccessibilityHitTest(location);
  if (hit) {
    // Ignore events on a frame or plug-in, because the touch events
    // will be re-targeted there and we don't want to fire duplicate
    // accessibility events.
    if (hit->GetLayoutObject() &&
        hit->GetLayoutObject()->IsLayoutEmbeddedContent())
      return;

    PostNotification(hit, ax::mojom::Event::kHover);
  }
}

void AXObjectCacheImpl::SetCanvasObjectBounds(HTMLCanvasElement* canvas,
                                              Element* element,
                                              const PhysicalRect& rect) {
  SCOPED_DISALLOW_LIFECYCLE_TRANSITION();

  AXObject* obj = GetOrCreate(element);
  if (!obj)
    return;

  AXObject* ax_canvas = GetOrCreate(canvas);
  if (!ax_canvas)
    return;

  obj->SetElementRect(rect, ax_canvas);
}

void AXObjectCacheImpl::AddPermissionStatusListener() {
  if (!document_->GetExecutionContext())
    return;

  // Passing an Origin to Mojo crashes if the host is empty because
  // blink::SecurityOrigin sets unique to false, but url::Origin sets
  // unique to true. This only happens for some obscure corner cases
  // like on Android where the system registers unusual protocol handlers,
  // and we don't need any special permissions in those cases.
  //
  // http://crbug.com/759528 and http://crbug.com/762716
  if (document_->Url().Protocol() != "file" &&
      document_->Url().Host().empty()) {
    return;
  }

  if (permission_service_.is_bound())
    permission_service_.reset();

  ConnectToPermissionService(
      document_->GetExecutionContext(),
      permission_service_.BindNewPipeAndPassReceiver(
          document_->GetTaskRunner(TaskType::kUserInteraction)));

  if (permission_observer_receiver_.is_bound())
    permission_observer_receiver_.reset();

  mojo::PendingRemote<mojom::blink::PermissionObserver> observer;
  permission_observer_receiver_.Bind(
      observer.InitWithNewPipeAndPassReceiver(),
      document_->GetTaskRunner(TaskType::kUserInteraction));
  permission_service_->AddPermissionObserver(
      CreatePermissionDescriptor(
          mojom::blink::PermissionName::ACCESSIBILITY_EVENTS),
      accessibility_event_permission_, std::move(observer));
}

void AXObjectCacheImpl::OnPermissionStatusChange(
    mojom::PermissionStatus status) {
  accessibility_event_permission_ = status;
}

bool AXObjectCacheImpl::CanCallAOMEventListeners() const {
  return accessibility_event_permission_ == mojom::PermissionStatus::GRANTED;
}

void AXObjectCacheImpl::RequestAOMEventListenerPermission() {
  if (accessibility_event_permission_ != mojom::PermissionStatus::ASK)
    return;

  if (!permission_service_.is_bound())
    return;

  permission_service_->RequestPermission(
      CreatePermissionDescriptor(
          mojom::blink::PermissionName::ACCESSIBILITY_EVENTS),
      LocalFrame::HasTransientUserActivation(document_->GetFrame()),
      WTF::BindOnce(&AXObjectCacheImpl::OnPermissionStatusChange,
                    WrapPersistent(this)));
}

void AXObjectCacheImpl::Trace(Visitor* visitor) const {
  visitor->Trace(agents_);
  visitor->Trace(document_);
  visitor->Trace(popup_document_);
  visitor->Trace(last_selected_from_active_descendant_);
  visitor->Trace(accessible_node_mapping_);
  visitor->Trace(layout_object_mapping_);
  visitor->Trace(node_object_mapping_);
  visitor->Trace(inline_text_box_object_mapping_);
  visitor->Trace(active_aria_modal_dialog_);

  visitor->Trace(objects_);
  visitor->Trace(notifications_to_post_main_);
  visitor->Trace(notifications_to_post_popup_);
  visitor->Trace(permission_service_);
  visitor->Trace(permission_observer_receiver_);
  visitor->Trace(tree_update_callback_queue_main_);
  visitor->Trace(tree_update_callback_queue_popup_);
  visitor->Trace(nodes_with_pending_children_changed_);
  visitor->Trace(nodes_with_spelling_or_grammar_markers_);
  visitor->Trace(nodes_for_subtree_removal_);
  visitor->Trace(render_accessibility_host_);
  visitor->Trace(ax_tree_source_);
  visitor->Trace(dirty_objects_);
  visitor->Trace(aria_notifications_);
  AXObjectCache::Trace(visitor);
}

ax::mojom::blink::EventFrom AXObjectCacheImpl::ComputeEventFrom() {
  if (active_event_from_ != ax::mojom::blink::EventFrom::kNone)
    return active_event_from_;

  if (document_ && document_->View() &&
      LocalFrame::HasTransientUserActivation(
          &(document_->View()->GetFrame()))) {
    return ax::mojom::blink::EventFrom::kUser;
  }

  return ax::mojom::blink::EventFrom::kPage;
}

WebAXAutofillState AXObjectCacheImpl::GetAutofillState(AXID id) const {
  auto iter = autofill_state_map_.find(id);
  if (iter == autofill_state_map_.end())
    return WebAXAutofillState::kNoSuggestions;
  return iter->value;
}

void AXObjectCacheImpl::SetAutofillState(AXID id, WebAXAutofillState state) {
  WebAXAutofillState previous_state = GetAutofillState(id);
  if (state != previous_state) {
    autofill_state_map_.Set(id, state);
    MarkAXObjectDirty(ObjectFromAXID(id));
  }
}

}  // namespace blink