Media Controls: make the MediaControlsOverlayPlayButton a runtime enabled flag.

third_party/WebKit/Source/web/WebRuntimeFeatures.cpp

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 374 matching lines @@
 }
 
 void WebRuntimeFeatures::enableRemotePlaybackAPI(bool enable) {
   RuntimeEnabledFeatures::setRemotePlaybackEnabled(enable);
 }
 
 void WebRuntimeFeatures::enableVideoFullscreenOrientationLock(bool enable) {
   RuntimeEnabledFeatures::setVideoFullscreenOrientationLockEnabled(enable);
 }
 
+void WebRuntimeFeatures::enableMediaControlsOverlayPlayButton(bool enable) {
+  RuntimeEnabledFeatures::setMediaControlsOverlayPlayButtonEnabled(enable);
+}
+
 }  // namespace blink