Add contentWindow attribute for <object> elements.

third_party/WebKit/Source/core/html/HTMLObjectElement.idl

 /*
  * Copyright (C) 2006, 2007, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  *
  * 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 16 matching lines @@
 ] interface HTMLObjectElement : HTMLElement {
     [Reflect, URL] attribute DOMString data;
     [Reflect] attribute DOMString type;
     // TODO(philipj): attribute boolean typeMustMatch;
     [Reflect] attribute DOMString name;
     [Reflect] attribute DOMString useMap;
     [ImplementedAs=formOwner] readonly attribute HTMLFormElement? form;
     [Reflect] attribute DOMString width;
     [Reflect] attribute DOMString height;
     [CheckSecurity=ReturnValue] readonly attribute Document? contentDocument;
-    // TODO(philipj): readonly attribute WindowProxy? contentWindow;
+    readonly attribute WindowProxy? contentWindow;

[Yuki, 2016/06/16 12:24:23]

Do we really support "WindowProxy"?

I don't see any other place that use WindowProxy.  For example,
HTMLIFrameElement.idl writes "Window?" instead of "WindowProxy?".

I know that the spec says it's WindowProxy, but I'm not sure if Blink really
supports it or not.

[Shanmuga Pandi, 2016/06/17 10:37:31]

Done.

     [CheckSecurity=ReturnValue, RaisesException] Document? getSVGDocument();
 
     readonly attribute boolean willValidate;
     readonly attribute ValidityState validity;
     readonly attribute DOMString validationMessage;
     boolean checkValidity();
     boolean reportValidity();
     void setCustomValidity(DOMString error);
 
     // TODO(philipj): legacycaller any (any... arguments); crbug.com/465009
@@ skipping 12 matching lines @@
     [Reflect] attribute DOMString codeType;
 
     [Reflect, TreatNullAs=EmptyString] attribute DOMString border;
 
     // TODO(philipj): These getters and setters are not in the spec.
     [Custom, NotEnumerable] getter boolean (unsigned long index);
     [Custom] setter boolean (unsigned long index, Node value);
     [Custom, NotEnumerable] getter Node (DOMString name);
     [Custom] setter Node (DOMString name, Node value);
 };