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

Source/core/dom/Document.idl

 /*
  * Copyright (C) 2006, 2007, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006, 2007 Samuel Weinig <sam@webkit.org>
  *
  * 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 185 matching lines @@
     [NotEnumerable] attribute EventListener ondrop;
     [NotEnumerable] attribute EventListener onerror;
     [NotEnumerable] attribute EventListener onfocus;
     [NotEnumerable] attribute EventListener oninput;
     [NotEnumerable] attribute EventListener oninvalid;
     [NotEnumerable] attribute EventListener onkeydown;
     [NotEnumerable] attribute EventListener onkeypress;
     [NotEnumerable] attribute EventListener onkeyup;
     [NotEnumerable] attribute EventListener onload;
     [NotEnumerable] attribute EventListener onmousedown;
+    [NotEnumerable] attribute EventListener onmouseenter;
+    [NotEnumerable] attribute EventListener onmouseleave;
     [NotEnumerable] attribute EventListener onmousemove;
     [NotEnumerable] attribute EventListener onmouseout;
     [NotEnumerable] attribute EventListener onmouseover;
     [NotEnumerable] attribute EventListener onmouseup;
     [NotEnumerable] attribute EventListener onmousewheel;
     [NotEnumerable] attribute EventListener onreadystatechange;
     [NotEnumerable] attribute EventListener onscroll;
     [NotEnumerable] attribute EventListener onselect;
     [NotEnumerable] attribute EventListener onsubmit;
 
@@ skipping 64 matching lines @@
     readonly attribute boolean webkitHidden;
 
     // Security Policy API: http://dvcs.w3.org/hg/content-security-policy/raw-file/tip/csp-specification.dev.html#script-interfaces
     [EnabledAtRuntime=experimentalContentSecurityPolicyFeatures] readonly attribute SecurityPolicy securityPolicy;
 
     readonly attribute HTMLScriptElement currentScript;
 };
 
 Document implements ParentNode;