Implement a Hit Test Cache.

Source/platform/geometry/LayoutRect.h

 /*
  * Copyright (c) 2012, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 218 matching lines @@
 inline IntRect pixelSnappedIntRect(const LayoutRect& rect)
 {
     return IntRect(roundedIntPoint(rect.location()), IntSize(
         snapSizeToPixel(rect.width(), rect.x()),
         snapSizeToPixel(rect.height(), rect.y())));
 }
 
 PLATFORM_EXPORT IntRect enclosingIntRect(const LayoutRect&);
 PLATFORM_EXPORT LayoutRect enclosingLayoutRect(const FloatRect&);
 
+// Returns a layout rect with minimum size for width and height that contains
+// |point|.
+PLATFORM_EXPORT LayoutRect boundingRect(const LayoutPoint&);
+
 inline IntRect pixelSnappedIntRect(LayoutUnit left, LayoutUnit top, LayoutUnit width, LayoutUnit height)
 {
     return IntRect(left.round(), top.round(), snapSizeToPixel(width, left), snapSizeToPixel(height, top));
 }
 
 inline IntRect pixelSnappedIntRectFromEdges(LayoutUnit left, LayoutUnit top, LayoutUnit right, LayoutUnit bottom)
 {
     return IntRect(left.round(), top.round(), snapSizeToPixel(right - left, left), snapSizeToPixel(bottom - top, top));
 }
 
 inline IntRect pixelSnappedIntRect(LayoutPoint location, LayoutSize size)
 {
     return IntRect(roundedIntPoint(location), pixelSnappedIntSize(size, location));
 }
 
 } // namespace blink
 
 #endif // LayoutRect_h