Generate and assign media track ids in demuxers.

media/base/media_tracks.cc

Index: media/base/media_tracks.cc
diff --git a/media/base/media_tracks.cc b/media/base/media_tracks.cc
index 770ab8dc7d4ed62110e0682def544dbfb517612f..afc8174328975abbc4a550dc2e9aa2e6c6c91309 100644
--- a/media/base/media_tracks.cc
+++ b/media/base/media_tracks.cc
@@ -15,30 +15,32 @@ MediaTracks::MediaTracks() {}
 
 MediaTracks::~MediaTracks() {}
 
-void MediaTracks::AddAudioTrack(const AudioDecoderConfig& config,
-                                StreamParser::TrackId byteStreamTrackId,
-                                const std::string& kind,
-                                const std::string& label,
-                                const std::string& language) {
+MediaTrack* MediaTracks::AddAudioTrack(const AudioDecoderConfig& config,
+                                       StreamParser::TrackId byteStreamTrackId,
+                                       const std::string& kind,
+                                       const std::string& label,
+                                       const std::string& language) {
   DCHECK(config.IsValidConfig());
   CHECK(audio_configs_.find(byteStreamTrackId) == audio_configs_.end());
   std::unique_ptr<MediaTrack> track = base::WrapUnique(new MediaTrack(
       MediaTrack::Audio, byteStreamTrackId, kind, label, language));
   tracks_.push_back(std::move(track));
   audio_configs_[byteStreamTrackId] = config;
+  return tracks_.back().get();
 }
 
-void MediaTracks::AddVideoTrack(const VideoDecoderConfig& config,
-                                StreamParser::TrackId byteStreamTrackId,
-                                const std::string& kind,
-                                const std::string& label,
-                                const std::string& language) {
+MediaTrack* MediaTracks::AddVideoTrack(const VideoDecoderConfig& config,
+                                       StreamParser::TrackId byteStreamTrackId,
+                                       const std::string& kind,
+                                       const std::string& label,
+                                       const std::string& language) {
   DCHECK(config.IsValidConfig());
   CHECK(video_configs_.find(byteStreamTrackId) == video_configs_.end());
   std::unique_ptr<MediaTrack> track = base::WrapUnique(new MediaTrack(
       MediaTrack::Video, byteStreamTrackId, kind, label, language));
   tracks_.push_back(std::move(track));
   video_configs_[byteStreamTrackId] = config;
+  return tracks_.back().get();

[xhwang, 2016/06/09 06:06:02]

nit: You can store a raw pointer of track.get() above, and return it here.

[servolk, 2016/06/09 19:14:46]

Done.

 }
 
 const AudioDecoderConfig& MediaTracks::getAudioConfig(