Implement a Hit Test Cache.

Source/core/dom/TreeScope.cpp

 /*
  * Copyright (C) 2011 Google Inc. All Rights Reserved.
  * Copyright (C) 2012 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.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 244 matching lines @@
     pointInDocument.moveBy(frameView->scrollPosition());
     IntPoint roundedPointInDocument = roundedIntPoint(pointInDocument);
 
     if (!frameView->visibleContentRect().contains(roundedPointInDocument))
         return false;
 
     point = roundedPointInDocument;
     return true;
 }
 
-HitTestResult hitTestInDocument(const Document* document, int x, int y)
+HitTestResult hitTestInDocument(const Document* document, int x, int y, const HitTestRequest& request)
 {
     IntPoint hitPoint(x, y);
     if (!pointWithScrollAndZoomIfPossible(*document, hitPoint))
         return HitTestResult();
 
-    HitTestRequest request(HitTestRequest::ReadOnly | HitTestRequest::Active);
     HitTestResult result(request, hitPoint);
     document->layoutView()->hitTest(result);
     return result;
 }
 
 Element* TreeScope::elementFromPoint(int x, int y) const
 {
-    HitTestResult result = hitTestInDocument(&rootNode().document(), x, y);
+    return hitTestPoint(x, y, HitTestRequest::ReadOnly | HitTestRequest::Active);
+}
+
+Element* TreeScope::hitTestPoint(int x, int y, const HitTestRequest& request) const
+{
+    HitTestResult result = hitTestInDocument(&rootNode().document(), x, y, request);
     Node* node = result.innerNode();
     if (!node || node->isDocumentNode())
         return 0;
     if (node->isPseudoElement() || node->isTextNode())
         node = node->parentOrShadowHostNode();
     ASSERT(!node || node->isElementNode() || node->isShadowRoot());
     node = ancestorInThisScope(node);
     if (!node || !node->isElementNode())
         return 0;
     return toElement(node);
@@ skipping 285 matching lines @@
     visitor->trace(m_parentTreeScope);
     visitor->trace(m_idTargetObserverRegistry);
     visitor->trace(m_selection);
     visitor->trace(m_elementsById);
     visitor->trace(m_imageMapsByName);
     visitor->trace(m_labelsByForAttribute);
     visitor->trace(m_scopedStyleResolver);
 }
 
 } // namespace blink