Enable HitTestCache by default.

Source/core/layout/HitTestResult.h

 /*
  * Copyright (C) 2006 Apple Computer, Inc.
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 48 matching lines @@
     HitTestResult(const HitTestRequest&, const LayoutPoint&);
     // Pass positive padding values to perform a rect-based hit test.
     HitTestResult(const HitTestRequest&, const LayoutPoint& centerPoint, unsigned topPadding, unsigned rightPadding, unsigned bottomPadding, unsigned leftPadding);
     HitTestResult(const HitTestRequest&, const HitTestLocation&);
     HitTestResult(const HitTestResult&);
     ~HitTestResult();
     HitTestResult& operator=(const HitTestResult&);
     DECLARE_TRACE();
 
     bool equalForCacheability(const HitTestResult&) const;
-    unsigned equalityScore(const HitTestResult&) const;
     void cacheValues(const HitTestResult&);
 
     // Populate this object based on another HitTestResult; similar to assignment operator
     // but don't assign any of the request parameters. ie. Thie method avoids setting
     // |m_hitTestLocation|, |m_hitTestRequest|.
     void populateFromCachedResult(const HitTestResult&);
 
     // For point-based hit tests, these accessors provide information about the node
     // under the point. For rect-based hit tests they are meaningless (reflect the
     // last candidate node observed in the rect).
@@ skipping 89 matching lines @@
     bool m_isOverWidget; // Returns true if we are over a widget (and not in the border/padding area of a LayoutPart for example).
 
     mutable OwnPtrWillBeMember<NodeSet> m_listBasedTestResult;
 };
 
 } // namespace blink
 
 WTF_ALLOW_CLEAR_UNUSED_SLOTS_WITH_MEM_FUNCTIONS(blink::HitTestResult);
 
 #endif // HitTestResult_h