Disable background video track behind a feature flag

third_party/WebKit/Source/core/html/HTMLMediaElement.h

 /*
  * 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
@@ skipping 376 matching lines @@
   void removeVideoTrack(WebMediaPlayer::TrackId) final;
   void addTextTrack(WebInbandTextTrack*) final;
   void removeTextTrack(WebInbandTextTrack*) final;
   void mediaSourceOpened(WebMediaSource*) final;
   void requestSeek(double) final;
   void remoteRouteAvailabilityChanged(WebRemotePlaybackAvailability) final;
   void connectedToRemoteDevice() final;
   void disconnectedFromRemoteDevice() final;
   void cancelledRemotePlaybackRequest() final;
   void remotePlaybackStarted() final;
+  bool hasSelectedVideoTrack() final;
+  WebMediaPlayer::TrackId getSelectedVideoTrackId() final;
   bool isAutoplayingMuted() final;
   void requestReload(const WebURL&) final;
 
   void loadTimerFired(TimerBase*);
   void progressEventTimerFired(TimerBase*);
   void playbackProgressTimerFired(TimerBase*);
   void startPlaybackProgressTimer();
   void startProgressEventTimer();
   void stopPeriodicTimers();
 
@@ skipping 308 matching lines @@
 
   AudioSourceProviderImpl m_audioSourceProvider;
 
   class AutoplayHelperClientImpl;
 
   friend class AutoplayUmaHelper;  // for isAutoplayAllowedPerSettings
   friend class Internals;
   friend class TrackDisplayUpdateScope;
   friend class AutoplayExperimentHelper;
   friend class MediaControlsTest;
+  friend class HTMLVideoElementTest;
 
   Member<AutoplayExperimentHelper::Client> m_autoplayHelperClient;
   Member<AutoplayExperimentHelper> m_autoplayHelper;
   Member<AutoplayUmaHelper> m_autoplayUmaHelper;
 
   WebRemotePlaybackClient* m_remotePlaybackClient;
 
   // class AutoplayVisibilityObserver;
   Member<ElementVisibilityObserver> m_autoplayVisibilityObserver;
 
   static URLRegistry* s_mediaStreamRegistry;
 };
 
 inline bool isHTMLMediaElement(const HTMLElement& element) {
   return isHTMLAudioElement(element) || isHTMLVideoElement(element);
 }
 
 DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(HTMLMediaElement);
 
 }  // namespace blink
 
 #endif  // HTMLMediaElement_h