Update popover=hint behavior to allow a stack of hints

The previous implementation only allowed one popover=hint to be open
at a time. Per conversation at [1], developers feel that it should be
possible to nest popover=hint popovers. This CL implements that
capability.

There are now two popover stacks in Document: PopoverAutoStack and
PopoverHintStack. Since it is possible to nest hints within autos,
the PopoverAutoStack can contain hints. However, there
are a few constraints:
 - The PopoverHintStack only ever contains hints.
 - Once the PopoverAutoStack contains a hint, all subsequent popovers
   in the stack must also be hints.
 - A popover=hint can never be the ancestor of a popover=auto.

The light dismiss behavior is roughly the same as before, with a
slight tweak that simplifies behavior: closing anything in the
PopoverAutoStack will always close everything in the PopoverHintStack.
That was not the case before, but it was a bit of a weird corner case.

Note that I found a crasher (happens in stable, with just auto
popovers) that I added a test for here. The bug for that is
crbug.com/1513282. I'll fix that in a followup.

[1] whatwg/html#9776 (comment)

Bug: 1416284,1513282
Change-Id: Ic064ecf1377bb8abfc812654c85016e6d1cbbdaf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5133909
Reviewed-by: Joey Arhar <jarhar@chromium.org>
Commit-Queue: Mason Freed <masonf@chromium.org>
Auto-Submit: Mason Freed <masonf@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1246573}

third_party/blink/renderer/core/dom/document.cc

@@ -8151,22 +8151,16 @@ HTMLDialogElement* Document::ActiveModalDialog() const {
   return nullptr;
 }
 
-void Document::SetPopoverHintShowing(HTMLElement* element) {
-  DCHECK(!element || element->HasPopoverAttribute());
-  DCHECK(RuntimeEnabledFeatures::HTMLPopoverHintEnabled());
-  popover_hint_showing_ = element;
-}
-
 HTMLElement* Document::TopmostPopoverOrHint() const {
-  if (PopoverHintShowing()) {
-    DCHECK(RuntimeEnabledFeatures::HTMLPopoverHintEnabled());
-    return PopoverHintShowing();
+  if (!PopoverHintStack().empty()) {
+    CHECK(RuntimeEnabledFeatures::HTMLPopoverHintEnabled());
+    return PopoverHintStack().back();
   }
-  if (PopoverStack().empty())
-    return nullptr;
-  return PopoverStack().back();
+  if (!PopoverAutoStack().empty()) {
+    return PopoverAutoStack().back();
+  }
+  return nullptr;
 }
-
 void Document::SetPopoverPointerdownTarget(const HTMLElement* popover) {
   DCHECK(!popover || popover->HasPopoverAttribute());
   popover_pointerdown_target_ = popover;
@@ -8902,8 +8896,8 @@ void Document::Trace(Visitor* visitor) const {
   visitor->Trace(node_lists_);
   visitor->Trace(top_layer_elements_);
   visitor->Trace(top_layer_elements_pending_removal_);
-  visitor->Trace(popover_stack_);
-  visitor->Trace(popover_hint_showing_);
+  visitor->Trace(popover_auto_stack_);
+  visitor->Trace(popover_hint_stack_);
   visitor->Trace(popover_pointerdown_target_);
   visitor->Trace(popovers_waiting_to_hide_);
   visitor->Trace(all_open_popovers_);

third_party/blink/renderer/core/dom/document.h

@@ -1577,15 +1577,20 @@ class CORE_EXPORT Document : public ContainerNode,
 
   HTMLDialogElement* ActiveModalDialog() const;
 
-  HTMLElement* PopoverHintShowing() const {
-    return popover_hint_showing_.Get();
+  const HeapVector<Member<HTMLElement>>& PopoverHintStack() const {
+    return popover_hint_stack_;
   }
-  void SetPopoverHintShowing(HTMLElement* element);
-  HeapVector<Member<HTMLElement>>& PopoverStack() { return popover_stack_; }
-  const HeapVector<Member<HTMLElement>>& PopoverStack() const {
-    return popover_stack_;
+  HeapVector<Member<HTMLElement>>& PopoverHintStack() {
+    return popover_hint_stack_;
   }
-  bool PopoverAutoShowing() const { return !popover_stack_.empty(); }
+  bool PopoverHintShowing() const { return !popover_hint_stack_.empty(); }
+  HeapVector<Member<HTMLElement>>& PopoverAutoStack() {
+    return popover_auto_stack_;
+  }
+  const HeapVector<Member<HTMLElement>>& PopoverAutoStack() const {
+    return popover_auto_stack_;
+  }
+  bool PopoverAutoShowing() const { return !popover_auto_stack_.empty(); }
   HeapHashSet<Member<HTMLElement>>& AllOpenPopovers() {
     return all_open_popovers_;
   }
@@ -2542,11 +2547,16 @@ class CORE_EXPORT Document : public ContainerNode,
   };
   VectorOf<TopLayerPendingRemoval> top_layer_elements_pending_removal_;
 
-  // The stack of currently-displayed `popover=auto` elements. Elements in the
-  // stack go from earliest (bottom-most) to latest (top-most).
-  HeapVector<Member<HTMLElement>> popover_stack_;
-  // The `popover=hint` that is currently showing, if any.
-  Member<HTMLElement> popover_hint_showing_;
+  // The stack of currently-displayed popover elements that descend from a root
+  // `popover=auto` element. Elements in the stack go from earliest
+  // (bottom-most) to latest (top-most). Note that `popover=hint` elements can
+  // exist in this stack, but there will never be a `popover=auto` that comes
+  // after that in the stack.
+  HeapVector<Member<HTMLElement>> popover_auto_stack_;
+  // The stack of currently-displayed `popover=hint` elements. Ordering in the
+  // stack is the same as for `popover_auto_stack_`. This stack will only ever
+  // contain `popover=hint` elements, and nothing else.
+  HeapVector<Member<HTMLElement>> popover_hint_stack_;
   // The popover (if any) that received the most recent pointerdown event.
   Member<const HTMLElement> popover_pointerdown_target_;
   // A set of popovers for which hidePopover() has been called, but animations

third_party/blink/renderer/core/fullscreen/fullscreen.cc

@@ -228,8 +228,7 @@ void GoFullscreen(Element& element,
   // If there are any open popovers, close them.
   HTMLElement::HideAllPopoversUntil(
       nullptr, document, HidePopoverFocusBehavior::kNone,
-      HidePopoverTransitionBehavior::kFireEventsAndWaitForTransitions,
-      HidePopoverIndependence::kHideUnrelated);
+      HidePopoverTransitionBehavior::kFireEventsAndWaitForTransitions);
 
   // To fullscreen an |element| within a |document|, set the |element|'s
   // fullscreen flag and add it to |document|'s top layer.

third_party/blink/renderer/core/html/html_dialog_element.cc

@@ -221,8 +221,7 @@ void HTMLDialogElement::show(ExceptionState& exception_state) {
   auto& document = GetDocument();
   HTMLElement::HideAllPopoversUntil(
       nullptr, document, HidePopoverFocusBehavior::kNone,
-      HidePopoverTransitionBehavior::kFireEventsAndWaitForTransitions,
-      HidePopoverIndependence::kHideUnrelated);
+      HidePopoverTransitionBehavior::kFireEventsAndWaitForTransitions);
 
   if (RuntimeEnabledFeatures::DialogNewFocusBehaviorEnabled()) {
     SetFocusForDialog();
@@ -320,8 +319,7 @@ void HTMLDialogElement::showModal(ExceptionState& exception_state) {
   // Showing a <dialog> should hide all open popovers.
   HTMLElement::HideAllPopoversUntil(
       nullptr, document, HidePopoverFocusBehavior::kNone,
-      HidePopoverTransitionBehavior::kFireEventsAndWaitForTransitions,
-      HidePopoverIndependence::kHideUnrelated);
+      HidePopoverTransitionBehavior::kFireEventsAndWaitForTransitions);
 
   if (RuntimeEnabledFeatures::DialogNewFocusBehaviorEnabled()) {
     SetFocusForDialog();