AX: Pre-size AXIsolatedObject::m_propertyMap to avoid unnecessary Has…

…hTable reallocations

https://bugs.webkit.org/show_bug.cgi?id=249873
rdar://problem/103687278

Reviewed by Chris Fleizach.

Use reserveInitialCapacity to give AXIsolatedObject::m_propertyMap an
initial size to help avoid unnecessary HashTable reallocations. These
HashTable reallocations showed up in `sample`s when using VoiceOver on
popular websites.

This patch also removes AXPropertyName::TagName since it's not used on
the Mac platform for any AX-client facing functionality (and Mac is the
only platform that enables isolated tree mode).

* Source/WebCore/accessibility/isolatedtree/AXIsolatedObject.cpp:
(WebCore::AXIsolatedObject::AXIsolatedObject):
(WebCore::AXIsolatedObject::initializeProperties):
(WebCore::AXIsolatedObject::tagName const):
* Source/WebCore/accessibility/isolatedtree/AXIsolatedObject.h:
* Source/WebCore/accessibility/isolatedtree/AXIsolatedTree.h:

Canonical link: https://commits.webkit.org/258328@main

Source/WebCore/accessibility/isolatedtree/AXIsolatedObject.cpp

@@ -50,6 +50,12 @@ AXIsolatedObject::AXIsolatedObject(const Ref<AXCoreObject>& axObject, AXIsolated
     m_parentID = axParent ? axParent->objectID() : AXID();
 
     auto isRoot = !axParent && axObject->isScrollView() ? IsRoot::Yes : IsRoot::No;
+
+    // Every object will have at least this many properties. We can shrink this number
+    // to some estimated average once we implement sparse property storage (i.e. only storing
+    // a property if it's not the default value for its type).
+    m_propertyMap.reserveInitialCapacity(126);
+
     initializeProperties(axObject, isRoot);
 }
 
@@ -178,7 +184,6 @@ void AXIsolatedObject::initializeProperties(const Ref<AXCoreObject>& coreObject,
     setProperty(AXPropertyName::Orientation, static_cast<int>(object.orientation()));
     setProperty(AXPropertyName::HierarchicalLevel, object.hierarchicalLevel());
     setProperty(AXPropertyName::Language, object.language().isolatedCopy());
-    setProperty(AXPropertyName::TagName, object.tagName().string().isolatedCopy());
     setProperty(AXPropertyName::SupportsLiveRegion, object.supportsLiveRegion());
     setProperty(AXPropertyName::IsInsideLiveRegion, object.isInsideLiveRegion());
     setProperty(AXPropertyName::LiveRegionStatus, object.liveRegionStatus().isolatedCopy());
@@ -1171,6 +1176,12 @@ bool AXIsolatedObject::performDefaultAction()
     return false;
 }
 
+AtomString AXIsolatedObject::tagName() const
+{
+    ASSERT_NOT_REACHED();
+    return AtomString();
+}
+
 bool AXIsolatedObject::isAccessibilityNodeObject() const
 {
     ASSERT_NOT_REACHED();

Source/WebCore/accessibility/isolatedtree/AXIsolatedObject.h

@@ -325,7 +325,7 @@ class AXIsolatedObject final : public AXCoreObject {
     void tabChildren(AccessibilityChildrenVector& children) override { fillChildrenVectorForProperty(AXPropertyName::TabChildren, children); }
     AccessibilityChildrenVector contents() override;
     bool hasARIAValueNow() const override { return boolAttributeValue(AXPropertyName::HasARIAValueNow); }
-    AtomString tagName() const override { return AtomString { stringAttributeValue(AXPropertyName::TagName) }; }
+    AtomString tagName() const override;
     const AccessibilityChildrenVector& children(bool updateChildrenIfNeeded = true) override;
     void updateChildrenIfNecessary() override;
     bool isDetachedFromParent() override;

Source/WebCore/accessibility/isolatedtree/AXIsolatedTree.h

@@ -253,7 +253,6 @@ enum class AXPropertyName : uint16_t {
     SupportsSetSize,
     TabChildren,
     TableLevel,
-    TagName,
     TextLength,
     Title,
     TitleAttributeValue,