Implement basic parts of hit regions on canvas2d.

Source/core/testing/Internals.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 262 matching lines @@
     void setValueForUser(Element element, DOMString value);
 
     DOMString textSurroundingNode(Node node, long x, long y, unsigned long maxLength);
 
     void setFocused(boolean focused);
 
     // These functions are for testing NetInfo. You must call setNetworkStateNotifierTestOnly(true)
     // before calling setNetworkConnectionInfo.
     void setNetworkStateNotifierTestOnly(boolean testOnly);
     [RaisesException] void setNetworkConnectionInfo(DOMString type);
+
+    // This function is for testing HitRegions on Canvas2D.
+    unsigned long countHitRegions(CanvasRenderingContext2D context);
 };