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 28 matching lines @@
         TouchEvent = 1 << 7,
         AllowChildFrameContent = 1 << 8,
         ChildFrameHitTest = 1 << 9,
         IgnorePointerEventsNone = 1 << 10,
         // Collect a list of nodes instead of just one.
         // (This is for elementsFromPoint and rect-based tests).
         ListBased = 1 << 11,
         // When using list-based testing, this flag causes us to continue hit
         // testing after a hit has been found.
         PenetratingList = 1 << 12,
+        AvoidCache = 1 << 13,
     };
 
     typedef unsigned HitTestRequestType;
 
     HitTestRequest(HitTestRequestType requestType)
         : m_requestType(requestType)
     {
         // Penetrating lists should also be list-based.
         ASSERT(!(requestType & PenetratingList) || (requestType & ListBased));
     }
 
     bool readOnly() const { return m_requestType & ReadOnly; }
     bool active() const { return m_requestType & Active; }
     bool move() const { return m_requestType & Move; }
     bool release() const { return m_requestType & Release; }
     bool ignoreClipping() const { return m_requestType & IgnoreClipping; }
     bool svgClipContent() const { return m_requestType & SVGClipContent; }
     bool touchEvent() const { return m_requestType & TouchEvent; }
     bool allowsChildFrameContent() const { return m_requestType & AllowChildFrameContent; }
     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; }
+    bool avoidCache() const { return m_requestType & AvoidCache; }
 
     // Convenience functions
     bool touchMove() const { return move() && touchEvent(); }
 
     HitTestRequestType type() const { return m_requestType; }
 
+    // The Cacheability bits don't affect hit testing computation.
+    // TODO(dtapuska): These bits really shouldn't be fields on the HitTestRequest as
+    // they don't influence the result; but rather are hints on the output as to what to do.
+    // Perhaps move these fields to another enum ?
+    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