Use [ImplementedAs=domWindow] for Document.defaultView()

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 68 matching lines @@
                                                       optional unsigned long whatToShow,
                                                       optional NodeFilter filter,
                                                       optional boolean expandEntityReferences);
     [RaisesException] TreeWalker createTreeWalker(Node root,
                                                   optional unsigned long whatToShow,
                                                   optional NodeFilter filter,
                                                   optional boolean expandEntityReferences);
 
     // DOM Level 2 Abstract Views (DocumentView interface)
 
-    readonly attribute Window defaultView;
+    [ImplementedAs=domWindow] readonly attribute Window defaultView;
 
     // DOM Level 2 Style (DocumentStyle interface)
 
     readonly attribute StyleSheetList styleSheets;
 
     // DOM Level 2 Style (DocumentCSS interface)
 
      CSSStyleDeclaration getOverrideStyle([Default=Undefined] optional Element element,
                                                         [Default=Undefined] optional DOMString pseudoElement);
 
@@ skipping 172 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
     [RuntimeEnabled=ExperimentalContentSecurityPolicyFeatures] readonly attribute SecurityPolicy securityPolicy;
 
     readonly attribute HTMLScriptElement currentScript;
 };
 
 Document implements ParentNode;