Add a custom element to own structure of shadow DOM plugin placeholders.

Source/core/testing/Internals.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 259 matching lines @@
     // before calling setNetworkConnectionInfo.
     void setNetworkStateNotifierTestOnly(boolean testOnly);
     [RaisesException] void setNetworkConnectionInfo(DOMString type);
 
     // This function is for testing HitRegions on Canvas2D.
     unsigned long countHitRegions(CanvasRenderingContext2D context);
 
     DOMString serializeNavigationMarkup();
     void hideAllTransitionElements();
 
-    [RaisesException] void forcePluginPlaceholder(HTMLElement plugin, DOMString htmlSource);
+    [RaisesException, TypeChecking=Interface] void forcePluginPlaceholder(HTMLElement plugin, DOMString htmlSource);
+    [RaisesException, TypeChecking=Interface] void forcePluginPlaceholder(HTMLElement plugin, Dictionary options);
 
     DictionaryTest dictionaryTest();
 };