Unship MediaController by making it an experimental runtime-enabled feature

Source/core/html/HTMLMediaElement.cpp

 /*
  * Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 414 matching lines @@
         else {
             // The spec does not define an "invalid value default" but "auto" is suggested as the
             // "missing value default", so use it for everything except "none" and "metadata"
             m_preload = MediaPlayer::Auto;
         }
 
         // The attribute must be ignored if the autoplay attribute is present
         if (!autoplay() && m_player)
             setPlayerPreload();
 
-    } else if (name == mediagroupAttr) {
+    } else if (name == mediagroupAttr && RuntimeEnabledFeatures::mediaControllerEnabled()) {
         setMediaGroup(value);
     } else {
         HTMLElement::parseAttribute(name, value);
     }
 }
 
 void HTMLMediaElement::finishParsingChildren()
 {
     HTMLElement::finishParsingChildren();
 
@@ skipping 3188 matching lines @@
 
 void HTMLMediaElement::trace(Visitor* visitor)
 {
     visitor->trace(m_textTracks);
     visitor->trace(m_textTracksWhenResourceSelectionBegan);
     Supplementable<HTMLMediaElement>::trace(visitor);
     HTMLElement::trace(visitor);
 }
 
 }