Reland "Improve slot a11y invalidation/cleanup"

This is a reland of commit dd9058a

Reason for revert: broke Fuchsia test expectations.
https://ci.chromium.org/p/chromium/builders/ci/fuchsia-arm64-cast-receiver-rel/3859. Fuchsia should not actually be picking up ignored nodes at all, and therefore it should not have regressed. I've filed a bug on Fuchsia to change that behavior: crbug.com/1420272

Patchset 1 contains the originally-landed code.

Original change's description:
> Improve slot a11y invalidation/cleanup
>
> Remove obscure logic related to determining if a slot is relevant, and just treat them all as relevant. I believe this was required to pass some PDF accessibility tests in the pass, but no longer seems to be. This causes a couple of changes to Blink expectations, but because the irrelevant slots are still hidden/ignored, the platform expectations are not changing, which is what's really important.
>
> As a result, we no longer leave extra objects in AXObjectCache or serializer when an there are changes related to slots. This is verified by a follow-up, CL:4185240, and this CL is necessary to pass the checks added there.
>
> Bug: None
>
> Change-Id: If787fcfc79a3568ffacc262d29f7cc4a5d89dbba
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4295193
> Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
> Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1110744}

Bug: None
Change-Id: Ic323ad86a57c6254659660979311636ff3bd213f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4294848
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Auto-Submit: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1111125}

content/test/data/accessibility/html/custom-element-hidden-expected-blink.txt

@@ -5,4 +5,7 @@ rootWebArea htmlTag='#document'
 ++++++genericContainer ignored invisible htmlTag='div'
 ++++++++genericContainer ignored invisible htmlTag='my-element'
 ++++++++++genericContainer ignored invisible htmlTag='div'
-++++++button htmlTag='button' name='Done'
+++++++++++++genericContainer ignored invisible htmlTag='slot'
+++++++++++++++genericContainer ignored invisible htmlTag='span'
+++++++++++++++++staticText ignored invisible name='Slot contents'
+++++++button htmlTag='button' name='Done'

content/test/data/accessibility/html/meter-expected-blink.txt

@@ -6,3 +6,5 @@ rootWebArea
 ++++++++++genericContainer
 ++++++++++++genericContainer ignored
 ++++++++genericContainer ignored invisible
+++++++++++genericContainer ignored invisible
+++++++++++++staticText ignored invisible name='2 out of 10'

content/test/data/accessibility/html/meter-expected-fuchsia.txt

@@ -5,4 +5,6 @@ UNKNOWN focusable has_input_focus
 ++++++++UNKNOWN
 ++++++++++UNKNOWN
 ++++++++++++UNKNOWN hidden
-++++++++UNKNOWN hidden
+++++++++UNKNOWN hidden
+++++++++++UNKNOWN hidden
+++++++++++++STATIC_TEXT hidden label='2 out of 10'

content/test/data/accessibility/html/popover-api-expected-blink.txt

@@ -10,6 +10,9 @@ rootWebArea
 ++++++++genericContainer ignored invisible
 ++++++++++staticText ignored invisible name='Listbox role on ul'
 ++++++details ignored invisible
+++++++++genericContainer ignored invisible
+++++++++++disclosureTriangle ignored invisible
+++++++++++++staticText ignored invisible name='summary/details popover'
 ++++++button collapsed name='Button pointing to hidden popover'
 ++++++++staticText name='Button pointing to hidden popover'
 ++++++++++inlineTextBox name='Button pointing to hidden popover'

content/test/data/accessibility/html/selectmenu-expected-blink.txt

@@ -12,10 +12,14 @@ rootWebArea focusable
 ++++++++++++++genericContainer ignored
 ++++++++genericContainer ignored
 ++++++++++listBox ignored invisible
+++++++++++++genericContainer ignored invisible
+++++++++++++++listBoxOption focusable ignored invisible
+++++++++++++++listBoxOption focusable ignored invisible
+++++++++++++++listBoxOption focusable ignored invisible
 ++++++genericContainer
 ++++++++genericContainer ignored
 ++++++++++comboBoxMenuButton collapsed value='Option 1' haspopup=listbox
 ++++++++++++staticText name='Custom selectmenu button'
 ++++++++++++++inlineTextBox name='Custom selectmenu button'
 ++++++++genericContainer ignored
-++++++++++listBox ignored invisible
+++++++++++listBox ignored invisible

content/test/data/accessibility/html/selectmenu-expected-fuchsia.txt

@@ -12,6 +12,10 @@ UNKNOWN focusable has_input_focus
 ++++++++++++++UNKNOWN hidden
 ++++++++UNKNOWN hidden
 ++++++++++UNKNOWN hidden
+++++++++++++UNKNOWN hidden
+++++++++++++++UNKNOWN hidden focusable actions='{DEFAULT}'
+++++++++++++++UNKNOWN hidden focusable actions='{DEFAULT}'
+++++++++++++++UNKNOWN hidden focusable actions='{DEFAULT}'
 ++++++UNKNOWN
 ++++++++UNKNOWN hidden
 ++++++++++UNKNOWN actions='{DEFAULT}' value='Option 1'

content/test/data/accessibility/regression/title-in-shadow-expected-blink.txt

@@ -6,3 +6,4 @@ rootWebArea name=''
 ++++++++++genericContainer
 ++++++++++++genericContainer ignored
 ++++++++genericContainer ignored invisible
+++++++++++genericContainer ignored invisible

third_party/blink/renderer/modules/accessibility/ax_node_object.cc

@@ -3177,18 +3177,9 @@ String AXNodeObject::GetValueForControl() const {
     if (auto* select_menu = HTMLSelectMenuElement::OwnerSelectMenu(node)) {
       DCHECK(RuntimeEnabledFeatures::HTMLSelectMenuElementEnabled());
       if (HTMLOptionElement* selected = select_menu->selectedOption()) {
-        // TODO(accessibility) Because these <option> elements can contain
-        // anything, we need to create an AXObject for the selected option, and
-        // use ax_selected_option->ComputedName(). However, for now, the
-        // AXObject is not created because AXObject::IsRelevantSlotElement()
-        // returns false for the invisible slot parent. Also, strangely,
-        // selected->innerText()/GetInnerTextWithoutUpdate() are returning "".
-        // See the following content_browsertest:
-        // All/DumpAccessibilityTreeTest.AccessibilitySelectMenu/blink.
-        // TODO(crbug.com/1401767): DCHECK fails with synchronous serialization.
-        DCHECK(selected->firstChild())
-            << "There is a selected option but it has no DOM children.";
-        return selected->textContent();
+        if (selected->firstChild()) {
+          return selected->textContent();
+        }
       }
       return String();
     }

third_party/blink/renderer/modules/accessibility/ax_object_cache_impl.cc

@@ -519,12 +519,6 @@ bool IsSubtreePrunedForAccessibility(const Element* 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()) {
@@ -1132,57 +1126,6 @@ bool AXObjectCacheImpl::ShouldCreateAXMenuListFor(LayoutObject* layout_object) {
   return false;
 }
 
-// static
-bool AXObjectCacheImpl::IsRelevantSlotElement(const HTMLSlotElement& slot) {
-  // 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 unless it is canvas fallback
-  // content. In order to detect this condition, we look to the first non-slot
-  // parent. If it has a layout object, the <slot>'s contents are rendered.
-  // If it doesn't, but it's in the canvas subtree, those contents should be
-  // treated as canvas fallback content.
-  //
-  // The alternative way to determine whether the <slot> is still relevant for
-  // rendering is to iterate FlatTreeTraversal::Parent until you get to the last
-  // parent, and see if it's a document. If it is not a document, then it is not
-  // relevant. This seems much slower than just checking GetLayoutObject() as it
-  // needs to iterate the parent chain. However, checking GetLayoutObject()
-  // could produce null in the case of something that is
-  // content-visibility:auto. This means that any slotted content inside
-  // content-visibility:auto may be removed from the AX tree depending on
-  // whether it was recently rendered.
-  //
-  // TODO(accessibility) This fails for the web test
-  // detach-locked-slot-children-crash.html with --force-renderer-accessibility.
-  // See web_tests/FlagExpectations/force-renderer-accessibility.
-  // There should be a better way to accomplish this.
-  // Could a new function be added to the slot element?
-  const Node* parent = LayoutTreeBuilderTraversal::Parent(slot);
-  if (const HTMLSlotElement* parent_slot =
-          ToHTMLSlotElementIfSupportsAssignmentOrNull(parent)) {
-    return AXObjectCacheImpl::IsRelevantSlotElement(*parent_slot);
-  }
-
-  if (parent && parent->GetLayoutObject())
-    return true;
-
-  const Element* parent_element = DynamicTo<Element>(parent);
-  if (!parent_element)
-    return false;
-
-  // Authors can include elements as "Fallback content" inside a <canvas> in
-  // order to provide an alternative means to interact with the canvas using
-  // a screen reader. Those should always be included.
-  if (parent_element->IsInCanvasSubtree())
-    return true;
-
-  // LayoutObject::CreateObject() will not create an object for elements
-  // with display:contents. If we do not include a <slot> for that reason,
-  // any descendants will be not be included in the accessibility tree.
-  return parent_element->HasDisplayContentsStyle();
-}
-
 // static
 bool AXObjectCacheImpl::IsRelevantPseudoElement(const Node& node) {
   DCHECK(node.IsPseudoElement());
@@ -3672,18 +3615,6 @@ AXObject* AXObjectCacheImpl::GetSerializationTarget(AXObject* obj) {
     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.

third_party/blink/renderer/modules/accessibility/ax_object_cache_impl.h

@@ -423,7 +423,6 @@ class MODULES_EXPORT AXObjectCacheImpl
   static bool IsRelevantPseudoElement(const Node& node);
   static bool IsRelevantPseudoElementDescendant(
       const LayoutObject& layout_object);
-  static bool IsRelevantSlotElement(const HTMLSlotElement& slot);
 
   bool HasBeenDisposed() { return has_been_disposed_; }