Use base::Optional for selected video track.

media/base/pipeline_impl.h

 // Copyright (c) 2016 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_BASE_PIPELINE_IMPL_H_
 #define MEDIA_BASE_PIPELINE_IMPL_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 77 matching lines @@
   float GetVolume() const override;
   void SetVolume(float volume) override;
   base::TimeDelta GetMediaTime() const override;
   Ranges<base::TimeDelta> GetBufferedTimeRanges() const override;
   base::TimeDelta GetMediaDuration() const override;
   bool DidLoadingProgress() override;
   PipelineStatistics GetStatistics() const override;
   void SetCdm(CdmContext* cdm_context,
               const CdmAttachedCB& cdm_attached_cb) override;
 
-  // |enabledTrackIds| contains track ids of enabled audio tracks.
+  // |enabled_track_ids| contains track ids of enabled audio tracks.
   void OnEnabledAudioTracksChanged(
-      const std::vector<MediaTrack::Id>& enabledTrackIds) override;
+      const std::vector<MediaTrack::Id>& enabled_track_ids) override;
 
-  // |trackId| either empty, which means no video track is selected, or contain
-  // one element - the selected video track id.
+  // |selected_track_id| is either empty, which means no video track is
+  // selected, or contains the selected video track id.
   void OnSelectedVideoTrackChanged(
-      const std::vector<MediaTrack::Id>& selectedTrackId) override;
+      base::Optional<MediaTrack::Id> selected_track_id) override;
 
  private:
   friend class MediaLog;
   class RendererWrapper;
 
   // Pipeline states, as described above.
   // TODO(alokp): Move this to RendererWrapper after removing the references
   // from MediaLog.
   enum State {
     kCreated,
@@ skipping 65 matching lines @@
 
   base::ThreadChecker thread_checker_;
   base::WeakPtrFactory<PipelineImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PipelineImpl);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_PIPELINE_IMPL_H_