AX: AccessibilityNodeObject never resets m_childrenDirty to false

https://bugs.webkit.org/show_bug.cgi?id=245322
rdar://problem/100073372

Reviewed by Chris Fleizach.

In https://bugs.webkit.org/show_bug.cgi?id=245212, we moved these
methods from AccessibilityRenderObject to AccessibilityNodeObject:

  - updateChildrenIfNecessary
  - setNeedsToUpdateChildren
  - needsToUpdateChildren
  - setNeedsToUpdateSubtree

But crucially, we did not move the implementation of clearChildren,
which is what resets m_childrenDirty to false when necessary, causing a
performance issue (not a correctness issue) for these objects.

* Source/WebCore/accessibility/AccessibilityNodeObject.cpp:
(WebCore::AccessibilityNodeObject::clearChildren):
* Source/WebCore/accessibility/AccessibilityNodeObject.h:
* Source/WebCore/accessibility/AccessibilityRenderObject.cpp:
(WebCore::AccessibilityRenderObject::clearChildren): Deleted.
* Source/WebCore/accessibility/AccessibilityRenderObject.h:

Canonical link: https://commits.webkit.org/254600@main

Source/WebCore/accessibility/AccessibilityNodeObject.cpp

@@ -455,6 +455,12 @@ void AccessibilityNodeObject::updateChildrenIfNecessary()
     AccessibilityObject::updateChildrenIfNecessary();
 }
 
+void AccessibilityNodeObject::clearChildren()
+{
+    AccessibilityObject::clearChildren();
+    m_childrenDirty = false;
+}
+
 void AccessibilityNodeObject::addChildren()
 {
     // If the need to add more children in addition to existing children arises, 

Source/WebCore/accessibility/AccessibilityNodeObject.h

@@ -164,6 +164,7 @@ class AccessibilityNodeObject : public AccessibilityObject {
     AccessibilityRole remapAriaRoleDueToParent(AccessibilityRole) const;
 
     void addChildren() override;
+    void clearChildren() override;
     void updateChildrenIfNecessary() override;
     bool canHaveChildren() const override;
     bool isDescendantOfBarrenParent() const override;

Source/WebCore/accessibility/AccessibilityRenderObject.cpp

@@ -2902,12 +2902,6 @@ bool AccessibilityRenderObject::canSetTextRangeAttributes() const
     return isTextControl();
 }
 
-void AccessibilityRenderObject::clearChildren()
-{
-    AccessibilityObject::clearChildren();
-    m_childrenDirty = false;
-}
-
 void AccessibilityRenderObject::addImageMapChildren()
 {
     RenderBoxModelObject* cssBox = renderBoxModelObject();

Source/WebCore/accessibility/AccessibilityRenderObject.h

@@ -133,8 +133,6 @@ class AccessibilityRenderObject : public AccessibilityNodeObject {
     AccessibilityChildrenVector documentLinks() override;
     FrameView* documentFrameView() const override;
 
-    void clearChildren() override;
-
     void setFocused(bool) override;
     void setSelectedTextRange(const PlainTextRange&) override;
     bool setValue(const String&) override;