Implement a Hit Test Cache.

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 45 matching lines @@
     HitTestResult();
     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;
+    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).
     // FIXME: Make these less error-prone for rect-based hit tests (center point or fail).
     Node* innerNode() const { return m_innerNode.get(); }
     Node* innerPossiblyPseudoNode() const { return m_innerPossiblyPseudoNode.get(); }
     Element* innerElement() const;
 
     // If innerNode is an image map or image map area, return the associated image node.
     Node* innerNodeOrImageMapImage() const;
@@ skipping 41 matching lines @@
     KURL absoluteImageURL() const;
     KURL absoluteMediaURL() const;
     KURL absoluteLinkURL() const;
     String textContent() const;
     bool isLiveLink() const;
     bool isMisspelled() const;
     bool isContentEditable() const;
 
     bool isOverLink() const;
 
+    const LayoutRect& validityRect() const { return m_validityRect; }
+    void setValidityRect(const LayoutRect&);
+
     // Return true if the test is a list-based test and we should continue testing.
     bool addNodeToListBasedTestResult(Node*, const HitTestLocation& pointInContainer, const LayoutRect& = LayoutRect());
     bool addNodeToListBasedTestResult(Node*, const HitTestLocation& pointInContainer, const FloatRect&);
     void append(const HitTestResult&);
 
     // If m_listBasedTestResult is 0 then set it to a new NodeSet. Return *m_listBasedTestResult. Lazy allocation makes
     // sense because the NodeSet is seldom necessary, and it's somewhat expensive to allocate and initialize. This method does
     // the same thing as mutableListBasedTestResult(), but here the return value is const.
     const NodeSet& listBasedTestResult() const;
 
     // Collapse the rect-based test result into a single target at the specified location.
     void resolveRectBasedTest(Node* resolvedInnerNode, const LayoutPoint& resolvedPointInMainFrame);
 
 private:
     NodeSet& mutableListBasedTestResult(); // See above.
     HTMLMediaElement* mediaElement() const;
 
     HitTestLocation m_hitTestLocation;
     HitTestRequest m_hitTestRequest;
+    LayoutRect m_validityRect;
 
     RefPtrWillBeMember<Node> m_innerNode;
     RefPtrWillBeMember<Node> m_innerPossiblyPseudoNode;
     // FIXME: Nothing changes this to a value different from m_hitTestLocation!
     LayoutPoint m_pointInInnerNodeFrame; // The hit-tested point in innerNode frame coordinates.
     LayoutPoint m_localPoint; // A point in the local coordinate space of m_innerNode's layoutObject. Allows us to efficiently
         // determine where inside the layoutObject we hit on subsequent operations.
     RefPtrWillBeMember<Element> m_innerURLElement;
     RefPtrWillBeMember<Scrollbar> m_scrollbar;
     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
 
 #endif // HitTestResult_h