Add contentWindow attribute for <object> elements.

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

Index: third_party/WebKit/Source/core/html/HTMLObjectElement.idl
diff --git a/third_party/WebKit/Source/core/html/HTMLObjectElement.idl b/third_party/WebKit/Source/core/html/HTMLObjectElement.idl
index d0f6261580a4b591d682c0f9e6f93c2a6df1a330..273c47c6ce019a4842ea661e0381b0ab9d62e547 100644
--- a/third_party/WebKit/Source/core/html/HTMLObjectElement.idl
+++ b/third_party/WebKit/Source/core/html/HTMLObjectElement.idl
@@ -34,7 +34,7 @@
     [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;