Use base::Optional for selected video track.

media/filters/ffmpeg_demuxer.h

 // Copyright (c) 2012 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.
 
 // Implements the Demuxer interface using FFmpeg's libavformat.  At this time
 // will support demuxing any audio/video format thrown at it.  The streams
 // output mime types audio/x-ffmpeg and video/x-ffmpeg and include an integer
 // key FFmpegCodecID which contains the CodecID enumeration value.  The CodecIDs
 // can be used to create and initialize the corresponding FFmpeg decoder.
 //
@@ skipping 221 matching lines @@
 
   // Allow FFmpegDemuxerStream to notify us when there is updated information
   // about capacity and what buffered data is available.
   void NotifyCapacityAvailable();
   void NotifyBufferingChanged();
 
   // Allow FFmpegDemxuerStream to notify us about an error.
   void NotifyDemuxerError(PipelineStatus error);
 
   void OnEnabledAudioTracksChanged(const std::vector<MediaTrack::Id>& track_ids,
-                                   base::TimeDelta currTime) override;
-  // |track_ids| is either empty or contains a single video track id.
-  void OnSelectedVideoTrackChanged(const std::vector<MediaTrack::Id>& track_ids,
-                                   base::TimeDelta currTime) override;
+                                   base::TimeDelta curr_time) override;
+  // |track_id| either contains the selected video track id or is null,
+  // indicating that all video tracks are deselected/disabled.
+  void OnSelectedVideoTrackChanged(base::Optional<MediaTrack::Id> track_id,
+                                   base::TimeDelta curr_time) override;
 
   // The lowest demuxed timestamp.  If negative, DemuxerStreams must use this to
   // adjust packet timestamps such that external clients see a zero-based
   // timeline.
   base::TimeDelta start_time() const { return start_time_; }
 
  private:
   // To allow tests access to privates.
   friend class FFmpegDemuxerTest;
 
@@ skipping 114 matching lines @@
   base::WeakPtr<FFmpegDemuxer> weak_this_;
   base::WeakPtrFactory<FFmpegDemuxer> cancel_pending_seek_factory_;
   base::WeakPtrFactory<FFmpegDemuxer> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(FFmpegDemuxer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_FFMPEG_DEMUXER_H_