Use base::Optional for selected video track.

media/filters/chunk_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.
 
 #ifndef MEDIA_FILTERS_CHUNK_DEMUXER_H_
 #define MEDIA_FILTERS_CHUNK_DEMUXER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 222 matching lines @@
 
   // Gets the currently buffered ranges for the specified ID.
   Ranges<base::TimeDelta> GetBufferedRanges(const std::string& id) const;
 
   // Gets the highest buffered PTS for the specified |id|. If there is nothing
   // buffered, returns base::TimeDelta().
   base::TimeDelta GetHighestPresentationTimestamp(const std::string& id) const;
 
   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,
+  // |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 currTime) override;
 
   // Appends media data to the source buffer associated with |id|, applying
   // and possibly updating |*timestamp_offset| during coded frame processing.
   // |append_window_start| and |append_window_end| correspond to the MSE spec's
   // similarly named source buffer attributes that are used in coded frame
   // processing. Returns true on success, false if the caller needs to run the
   // append error algorithm with decode error parameter set to true.
   bool AppendData(const std::string& id,
                   const uint8_t* data,
@@ skipping 200 matching lines @@
   int detected_text_track_count_;
 
   std::map<MediaTrack::Id, ChunkDemuxerStream*> track_id_to_demux_stream_map_;
 
   DISALLOW_COPY_AND_ASSIGN(ChunkDemuxer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_CHUNK_DEMUXER_H_