Disable background video track behind a feature flag

content/renderer/media/webmediaplayer_ms_unittest.cc

Index: content/renderer/media/webmediaplayer_ms_unittest.cc
diff --git a/content/renderer/media/webmediaplayer_ms_unittest.cc b/content/renderer/media/webmediaplayer_ms_unittest.cc
index ca98f859cd60f99000aa6a9e424fb4291e024b3a..3e9b5524be98cdadd1a25215d802915179b88d14 100644
--- a/content/renderer/media/webmediaplayer_ms_unittest.cc
+++ b/content/renderer/media/webmediaplayer_ms_unittest.cc
@@ -432,6 +432,10 @@ class WebMediaPlayerMSTest
   void remotePlaybackStarted() override {}
   bool isAutoplayingMuted() override { return false; }
   void requestReload(const blink::WebURL& newUrl) override {}
+  bool hasSelectedVideoTrack() override { return false; }
+  blink::WebMediaPlayer::TrackId getSelectedVideoTrackId() override {
+    return blink::WebMediaPlayer::TrackId();
+  }
 
   // Implementation of cc::VideoFrameProvider::Client
   void StopUsingProvider() override;