Implement a Hit Test Cache.

Source/core/layout/HitTestRequest.h

 /*
  * Copyright (C) 2006 Apple Computer, Inc.
  * Copyright (C) 2009 Torch Mobile Inc. http://www.torchmobile.com/
  * Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 57 matching lines @@
     bool isChildFrameHitTest() const { return m_requestType & ChildFrameHitTest; }
     bool ignorePointerEventsNone() const { return m_requestType & IgnorePointerEventsNone; }
     bool listBased() const { return m_requestType & ListBased; }
     bool penetratingList() const { return m_requestType & PenetratingList; }
 
     // Convenience functions
     bool touchMove() const { return move() && touchEvent(); }
 
     HitTestRequestType type() const { return m_requestType; }
 
+    static const HitTestRequestType CacheabilityBits = ReadOnly | Active | Move | Release | TouchEvent;
+    bool equalForCacheability(const HitTestRequest& value) const
+    {
+        return (m_requestType | CacheabilityBits) == (value.m_requestType | CacheabilityBits);
+    }
+
 private:
     HitTestRequestType m_requestType;
 };
 
 } // namespace blink
 
 #endif // HitTestRequest_h