MediaStream audio object graph untangling and clean-ups.

content/renderer/media/media_stream_audio_track.cc

 // Copyright 2014 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 "content/renderer/media/media_stream_audio_track.h"
 
 #include "base/logging.h"
 #include "third_party/WebKit/public/platform/WebMediaStreamSource.h"
 #include "third_party/webrtc/api/mediastreaminterface.h"
 
 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_callback_.is_null())
+      << "BUG: Subclass must ensure Stop() is called.";
 }
 
 // static
-MediaStreamAudioTrack* MediaStreamAudioTrack::GetTrack(
+MediaStreamAudioTrack* MediaStreamAudioTrack::From(
     const blink::WebMediaStreamTrack& track) {
   if (track.isNull() ||
       track.source().type() != blink::WebMediaStreamSource::TypeAudio) {
     return nullptr;
   }
   return static_cast<MediaStreamAudioTrack*>(track.extraData());
 }
 
+void MediaStreamAudioTrack::Start(const base::Closure& stop_callback) {
+  DCHECK(main_render_thread_checker_.CalledOnValidThread());
+  DCHECK(stop_callback_.is_null());
+  DVLOG(1) << "MediaStreamAudioTrack::Start()";
+  stop_callback_ = stop_callback;

[o1ka, 2016/03/02 16:31:14]

Do you intentionally allow passing null as stop_callback?

[miu, 2016/03/02 23:38:10]

Done.  Added DCHECK.

+}
+
+void MediaStreamAudioTrack::Stop() {
+  DCHECK(main_render_thread_checker_.CalledOnValidThread());
+  DVLOG(1) << "MediaStreamAudioTrack::Stop()";
+  if (!stop_callback_.is_null())
+    stop_callback_.Run();

[o1ka, 2016/03/02 16:31:14]

Do you want to reset the callback probably?

[miu, 2016/03/02 23:38:10]

Good catch!  Yes, I do.  Done.

+  OnStop();
+}
+
+void MediaStreamAudioTrack::OnStop() {}
+
 webrtc::AudioTrackInterface* MediaStreamAudioTrack::GetAudioAdapter() {
   NOTREACHED();
   return nullptr;
 }
 
 }  // namespace content