[Media] Add a finch trial param for background MediaSource videos

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 663 matching lines @@
   // when a preroll attempt began.
   bool preroll_attempt_pending_;
   base::TimeTicks preroll_attempt_start_time_;
 
   std::unique_ptr<base::TickClock> tick_clock_;
 
   // Monitors the player events.
   base::WeakPtr<MediaObserver> observer_;
 
   // The maximum video keyframe distance that allows triggering background
-  // playback optimizations.
+  // playback optimizations (non-MSE).
   base::TimeDelta max_keyframe_distance_to_disable_background_video_;
 
+  // The maximum video keyframe distance that allows triggering background
+  // playback optimizations (MSE).
+  base::TimeDelta max_keyframe_distance_to_disable_background_video_mse_;
+
   // When MSE memory pressure based garbage collection is enabled, the
   // |enable_instant_source_buffer_gc| controls whether the GC is done
   // immediately on memory pressure notification or during the next SourceBuffer
   // append (slower, but MSE spec compliant).
   bool enable_instant_source_buffer_gc_ = false;
 
   // Whether disabled the video track as an optimization.
   bool video_track_disabled_ = false;
 
   // Whether the pipeline is being resumed at the moment.
@@ skipping 19 matching lines @@
   base::TimeDelta last_uploaded_frame_timestamp_;
 
   base::CancelableCallback<void(base::TimeTicks)> frame_time_report_cb_;
 
   DISALLOW_COPY_AND_ASSIGN(WebMediaPlayerImpl);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BLINK_WEBMEDIAPLAYER_IMPL_H_