Don't expose WebKitShadowRoot constructor.

Source/core/frame/Window.idl

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Google 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.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 212 matching lines @@
     [Conditional=WEB_AUDIO, RuntimeEnabled=WebAudio] attribute AudioContextConstructor AudioContext;
     [Conditional=WEB_AUDIO, RuntimeEnabled=WebAudio] attribute OfflineAudioContextConstructor OfflineAudioContext;
     [RuntimeEnabled=PeerConnection] attribute RTCPeerConnectionConstructor webkitRTCPeerConnection;
     [RuntimeEnabled=ScriptedSpeech] attribute SpeechGrammarConstructor webkitSpeechGrammar;
     [RuntimeEnabled=ScriptedSpeech] attribute SpeechGrammarListConstructor webkitSpeechGrammarList;
     [RuntimeEnabled=ScriptedSpeech] attribute SpeechRecognitionConstructor webkitSpeechRecognition;
     [RuntimeEnabled=ScriptedSpeech] attribute SpeechRecognitionErrorConstructor webkitSpeechRecognitionError;
     [RuntimeEnabled=ScriptedSpeech] attribute SpeechRecognitionEventConstructor webkitSpeechRecognitionEvent;
     [Conditional=WEB_AUDIO] attribute PannerNodeConstructor webkitAudioPannerNode;
 
-    // Prefixed ShadowRoot constructor should be phased out eventually, but for the moment it must be always exposed.
-    // Unprefixed ShadowRoot constructor should be visible when the feature flag is enabled.
-    // FIXME: When it's ready to remove WebKitShadowRoot, get rid of both constructors from Window.idl and remove
-    // [NoInterfaceObject] from ShadowRoot interface definition.
-    attribute ShadowRootConstructor ShadowRoot;
-    [MeasureAs=PrefixedShadowRootConstructor] attribute ShadowRootConstructor WebKitShadowRoot;
-
     // window.toString() requires special handling in V8
     [DoNotCheckSignature, DoNotCheckSecurity, Custom, NotEnumerable] DOMString toString();
 
     [NotEnumerable] getter Window (unsigned long index);
     [Custom, NotEnumerable] getter Window (DOMString name);
 };
 
 Window implements GlobalEventHandlers;
 Window implements ImageBitmapFactories;
 Window implements WindowBase64;
 Window implements WindowEventHandlers;
 Window implements WindowTimers;