Implement a Hit Test Cache.

Source/core/testing/Internals.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple 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.
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     [RaisesException, TypeChecking=Interface] boolean isValidContentSelect(Element contentElement);
     [TypeChecking=Interface] Node treeScopeRootNode(Node node);
     [TypeChecking=Interface] Node parentTreeScope(Node node);
     [RaisesException, TypeChecking=Interface] boolean hasSelectorForIdInShadow(Element host, DOMString id);
     [RaisesException, TypeChecking=Interface] boolean hasSelectorForClassInShadow(Element host, DOMString className);
     [RaisesException, TypeChecking=Interface] boolean hasSelectorForAttributeInShadow(Element host, DOMString attributeName);
     [RaisesException, TypeChecking=Interface] unsigned short compareTreeScopePosition(Node treeScope1, Node treeScope2);
     [RaisesException] unsigned long updateStyleAndReturnAffectedElementCount();
     [RaisesException] unsigned long needsLayoutCount();
     [RaisesException] unsigned long hitTestCount(Document document);
+    [RaisesException] unsigned long hitTestCacheHits(Document document);
+    [RaisesException] Element? elementFromPointNoCache(Document document, double x, double y);
+    [RaisesException] void clearHitTestCache(Document document);
 
     // CSS Animation and Transition testing.
     [RaisesException] void pauseAnimations(double pauseTime);
 
     // Modifies m_desiredFrameStartTime in BitmapImage to advance the next frame time
     // for testing whether animated images work properly.
     [RaisesException] void advanceTimeForImage(Element image, double deltaTimeInSeconds);
 
     [RaisesException, TypeChecking=Interface] Node nextSiblingInComposedTree(Node node);
     [RaisesException, TypeChecking=Interface] Node firstChildInComposedTree(Node node);
@@ skipping 237 matching lines @@
 
     boolean isUseCounted(Document document, long useCounterId);
 
     iterable<long>;
 
     [Unscopeable] readonly attribute DOMString unscopeableAttribute;
     [Unscopeable] DOMString unscopeableMethod();
 
     ClientRectList focusRingRects(Element element);
 };