Allow muting/unmuting audio through media track API

media/base/media_tracks.cc

 // 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.
 
 #include "media/base/media_tracks.h"
 
 #include "base/bind.h"
 #include "media/base/audio_decoder_config.h"
 #include "media/base/video_decoder_config.h"
 
 namespace media {
 
 MediaTracks::MediaTracks() {}
 
 MediaTracks::~MediaTracks() {}
 
-void MediaTracks::AddAudioTrack(const AudioDecoderConfig& config,
-                                const std::string& id,
-                                const std::string& kind,
-                                const std::string& label,
-                                const std::string& language) {
+const MediaTrack* MediaTracks::AddAudioTrack(const AudioDecoderConfig& config,
+                                             const std::string& id,
+                                             const std::string& kind,
+                                             const std::string& label,
+                                             const std::string& language) {
   DCHECK(config.IsValidConfig());
   CHECK(audio_configs_.find(id) == audio_configs_.end());
   scoped_ptr<MediaTrack> track = make_scoped_ptr(
       new MediaTrack(MediaTrack::Audio, id, kind, label, language));
   tracks_.push_back(std::move(track));
   audio_configs_[id] = config;
+  return tracks_.back().get();
 }
 
-void MediaTracks::AddVideoTrack(const VideoDecoderConfig& config,
-                                const std::string& id,
-                                const std::string& kind,
-                                const std::string& label,
-                                const std::string& language) {
+const MediaTrack* MediaTracks::AddVideoTrack(const VideoDecoderConfig& config,
+                                             const std::string& id,
+                                             const std::string& kind,
+                                             const std::string& label,
+                                             const std::string& language) {
   DCHECK(config.IsValidConfig());
   CHECK(video_configs_.find(id) == video_configs_.end());
   scoped_ptr<MediaTrack> track = make_scoped_ptr(
       new MediaTrack(MediaTrack::Video, id, kind, label, language));
   tracks_.push_back(std::move(track));
   video_configs_[id] = config;
+  return tracks_.back().get();
 }
 
 const AudioDecoderConfig& MediaTracks::getAudioConfig(
     const std::string& id) const {
   auto it = audio_configs_.find(id);
   if (it != audio_configs_.end())
     return it->second;
   static AudioDecoderConfig invalidConfig;
   return invalidConfig;
 }
@@ skipping 21 matching lines @@
   for (const auto& track : tracks()) {
     if (track->type() == MediaTrack::Video) {
       return getVideoConfig(track->id());
     }
   }
   static VideoDecoderConfig invalidConfig;
   return invalidConfig;
 }
 
 }  // namespace media