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

Source/core/dom/EventNames.h

 /*
  * Copyright (C) 2005, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Jon Shier (jshier@iastate.edu)
  *
  * 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 74 matching lines @@
     macro(keypress) \
     macro(keyup) \
     macro(levelchange) \
     macro(load) \
     macro(loading) \
     macro(loadingdone) \
     macro(loadstart) \
     macro(message) \
     macro(midimessage) \
     macro(mousedown) \
+    macro(mouseenter) \
+    macro(mouseleave) \
     macro(mousemove) \
     macro(mouseout) \
     macro(mouseover) \
     macro(mouseup) \
     macro(mousewheel) \
     macro(noupdate) \
     macro(obsolete) \
     macro(offline) \
     macro(online) \
     macro(open) \
@@ skipping 216 matching lines @@
     };
 
     inline EventNames& eventNames()
     {
         return threadGlobalData().eventNames();
     }
 
 }
 
 #endif