Disable background video track behind a feature flag

media/blink/webmediaplayer_impl.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_BLINK_WEBMEDIAPLAYER_IMPL_H_
 #define MEDIA_BLINK_WEBMEDIAPLAYER_IMPL_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 339 matching lines @@
   // accessed on the media thread.
   void ReportMemoryUsage();
   void FinishMemoryUsageReport(int64_t demuxer_memory_usage);
 
   // Called during OnHidden() when we want a suspended player to enter the
   // paused state after some idle timeout.
   void ScheduleIdlePauseTimer();
 
   void CreateWatchTimeReporter();
 
+  // Returns true if the player is hidden.
+  bool IsHidden() const;
+
   blink::WebLocalFrame* frame_;
 
   // The playback state last reported to |delegate_|, to avoid setting duplicate
   // states. (Which can have undesired effects like resetting the idle timer.)
   DelegateState delegate_state_;
 
   // Set when OnSuspendRequested() is called with |must_suspend| unset.
   bool is_idle_;
 
   // Set when OnSuspendRequested() is called with |must_suspend| set.
@@ skipping 205 matching lines @@
 
   // Whether the player is currently in autoplay muted state.
   bool autoplay_muted_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(WebMediaPlayerImpl);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BLINK_WEBMEDIAPLAYER_IMPL_H_