Implement a Hit Test Cache.

Source/core/layout/LayoutObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 2640 matching lines @@
             inside = nodeAtPoint(result, locationInContainer, accumulatedOffset, HitTestChildBlockBackgrounds);
     }
 
     // See if the mouse is inside us but not any of our descendants
     if (hitTestFilter != HitTestDescendants && !inside)
         inside = nodeAtPoint(result, locationInContainer, accumulatedOffset, HitTestBlockBackground);
 
     return inside;
 }
 
-void LayoutObject::updateHitTestResult(HitTestResult& result, const LayoutPoint& point)
+void LayoutObject::updateHitTestResult(HitTestResult& result, const LayoutPoint& point, const LayoutRect& rect)
 {
     if (result.innerNode())
         return;
 
+    result.intersectValidityRect(rect);
     Node* node = this->node();
 
     // If we hit the anonymous layoutObjects inside generated content we should
     // actually hit the generated content so walk up to the PseudoElement.
     if (!node && parent() && parent()->isBeforeOrAfterContent()) {
         for (LayoutObject* layoutObject = parent(); layoutObject && !node; layoutObject = layoutObject->parent())
             node = layoutObject->node();
     }
 
     if (node)
@@ skipping 619 matching lines @@
         const blink::LayoutObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
     } else {
         fprintf(stderr, "Cannot showLayoutTree. Root is (nil)\n");
     }
 }
 
 #endif