MediaStream audio object graph untangling and clean-ups.

content/renderer/media/media_stream_audio_track.cc

Index: content/renderer/media/media_stream_audio_track.cc
diff --git a/content/renderer/media/media_stream_audio_track.cc b/content/renderer/media/media_stream_audio_track.cc
index 278ab05bb107369cdd23614565470e40846a3518..8477e9c11ce289eed34d3e19dc14d7fdd83b6012 100644
--- a/content/renderer/media/media_stream_audio_track.cc
+++ b/content/renderer/media/media_stream_audio_track.cc
@@ -12,13 +12,19 @@ namespace content {
 
 MediaStreamAudioTrack::MediaStreamAudioTrack(bool is_local_track)
     : MediaStreamTrack(is_local_track) {
+  DVLOG(1) << "MediaStreamAudioTrack::MediaStreamAudioTrack(is a "
+           << (is_local_track ? "local" : "remote") << " track)";
 }
 
 MediaStreamAudioTrack::~MediaStreamAudioTrack() {
+  DCHECK(main_render_thread_checker_.CalledOnValidThread());
+  DVLOG(1) << "MediaStreamAudioTrack::~MediaStreamAudioTrack()";
+  DCHECK(stop_callbacks_.empty())
+      << "BUG: Subclass must ensure WillStopTrack() is called.";
 }
 
 // static
-MediaStreamAudioTrack* MediaStreamAudioTrack::GetTrack(
+MediaStreamAudioTrack* MediaStreamAudioTrack::From(
     const blink::WebMediaStreamTrack& track) {
   if (track.isNull() ||
       track.source().type() != blink::WebMediaStreamSource::TypeAudio) {
@@ -27,6 +33,23 @@ MediaStreamAudioTrack* MediaStreamAudioTrack::GetTrack(
   return static_cast<MediaStreamAudioTrack*>(track.extraData());
 }
 
+void MediaStreamAudioTrack::AddStopObserver(
+    const base::Closure& stop_callback) {
+  DCHECK(main_render_thread_checker_.CalledOnValidThread());
+  DCHECK(!stop_callback.is_null());
+  DVLOG(1) << "MediaStreamAudioTrack::AddStopObserver()";
+  stop_callbacks_.push_back(stop_callback);
+}
+
+void MediaStreamAudioTrack::WillStopTrack() {
+  DCHECK(main_render_thread_checker_.CalledOnValidThread());
+  DVLOG(1) << "MediaStreamAudioTrack::WillStopTrack()";
+  std::vector<base::Closure> callbacks_to_run;
+  callbacks_to_run.swap(stop_callbacks_);
+  for (const base::Closure& callback : callbacks_to_run)
+    callback.Run();
+}
+
 webrtc::AudioTrackInterface* MediaStreamAudioTrack::GetAudioAdapter() {
   NOTREACHED();
   return nullptr;