Allow muting/unmuting audio through media track API

media/base/media_tracks.h

 // Copyright 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_MEDIA_TRACKS_H_
 #define MEDIA_BASE_MEDIA_TRACKS_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "media/base/media_export.h"
 #include "media/base/media_track.h"
 
 namespace media {
 
 class AudioDecoderConfig;
 class VideoDecoderConfig;
 
 class MEDIA_EXPORT MediaTracks {
  public:
   typedef std::vector<scoped_ptr<MediaTrack>> MediaTracksCollection;
 
   MediaTracks();
   ~MediaTracks();
 
   // Callers need to ensure that track id is unique.
-  void AddAudioTrack(const AudioDecoderConfig& config,
-                     const std::string& id,
-                     const std::string& kind,
-                     const std::string& label,
-                     const std::string& language);
+  const MediaTrack* AddAudioTrack(const AudioDecoderConfig& config,
+                                  const std::string& id,
+                                  const std::string& kind,
+                                  const std::string& label,
+                                  const std::string& language);
   // Callers need to ensure that track id is unique.
-  void AddVideoTrack(const VideoDecoderConfig& config,
-                     const std::string& id,
-                     const std::string& kind,
-                     const std::string& label,
-                     const std::string& language);
+  const MediaTrack* AddVideoTrack(const VideoDecoderConfig& config,
+                                  const std::string& id,
+                                  const std::string& kind,
+                                  const std::string& label,
+                                  const std::string& language);
 
   const MediaTracksCollection& tracks() const { return tracks_; }
 
   const AudioDecoderConfig& getAudioConfig(const std::string& id) const;
   const VideoDecoderConfig& getVideoConfig(const std::string& id) const;
 
   // TODO(servolk): These are temporary helpers useful until all code paths are
   // converted to properly handle multiple media tracks.
   const AudioDecoderConfig& getFirstAudioConfig() const;
   const VideoDecoderConfig& getFirstVideoConfig() const;
 
  private:
   MediaTracksCollection tracks_;
   std::map<std::string, AudioDecoderConfig> audio_configs_;
   std::map<std::string, VideoDecoderConfig> video_configs_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaTracks);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_MEDIA_TRACKS_H_