Implement 'mouseenter' and 'mouseleave' from DOM Level 3 Events.

Source/core/page/Window.idl

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2011 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 189 matching lines @@
     attribute EventListener oninvalid;
     attribute EventListener onkeydown;
     attribute EventListener onkeypress;
     attribute EventListener onkeyup;
     attribute EventListener onload;
     attribute EventListener onloadeddata;
     attribute EventListener onloadedmetadata;
     attribute EventListener onloadstart;
     attribute EventListener onmessage;
     attribute EventListener onmousedown;
+    attribute EventListener onmouseenter;
+    attribute EventListener onmouseleave;
     attribute EventListener onmousemove;
     attribute EventListener onmouseout;
     attribute EventListener onmouseover;
     attribute EventListener onmouseup;
     attribute EventListener onmousewheel;
     attribute EventListener onoffline;
     attribute EventListener ononline;
     attribute EventListener onpagehide;
     attribute EventListener onpageshow;
     attribute EventListener onpause;
@@ skipping 83 matching lines @@
 
     // window.toString() requires special handling in V8
     [DoNotCheckSignature, DoNotCheckSecurity, Custom, NotEnumerable] DOMString toString();
 
     [ImplementedAs=anonymousIndexedGetter, NotEnumerable] getter Window(unsigned long index);
     [Custom, NotEnumerable] getter Window (DOMString name);
 };
 
 Window implements WindowTimers;