Disable background video track behind a feature flag

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

Index: third_party/WebKit/Source/core/html/HTMLMediaElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLMediaElement.h b/third_party/WebKit/Source/core/html/HTMLMediaElement.h
index a4aae0c4f202d3135d9832a01dc30e160b345ac3..781569bcd23f917d32c78a68caef3a1b976ad2d7 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.h
@@ -394,6 +394,8 @@ class CORE_EXPORT HTMLMediaElement : public HTMLElement,
   void disconnectedFromRemoteDevice() final;
   void cancelledRemotePlaybackRequest() final;
   void remotePlaybackStarted() final;
+  bool hasSelectedVideoTrack() final;
+  WebMediaPlayer::TrackId getSelectedVideoTrackId() final;
   bool isAutoplayingMuted() final;
   void requestReload(const WebURL&) final;
 
@@ -722,6 +724,7 @@ class CORE_EXPORT HTMLMediaElement : public HTMLElement,
   friend class TrackDisplayUpdateScope;
   friend class AutoplayExperimentHelper;
   friend class MediaControlsTest;
+  friend class HTMLVideoElementTest;
 
   Member<AutoplayExperimentHelper::Client> m_autoplayHelperClient;
   Member<AutoplayExperimentHelper> m_autoplayHelper;