MediaStream audio object graph untangling and clean-ups.

content/renderer/media/webrtc/media_stream_remote_audio_track.cc

Index: content/renderer/media/webrtc/media_stream_remote_audio_track.cc
diff --git a/content/renderer/media/webrtc/media_stream_remote_audio_track.cc b/content/renderer/media/webrtc/media_stream_remote_audio_track.cc
index 17df845f81c491b3c9a0631d3a20835f1b05aa1a..84b89fe2dedda731f2dd7f6804e15908904a1517 100644
--- a/content/renderer/media/webrtc/media_stream_remote_audio_track.cc
+++ b/content/renderer/media/webrtc/media_stream_remote_audio_track.cc
@@ -8,6 +8,8 @@
 
 #include <list>
 
+#include "base/bind.h"
+#include "base/bind_helpers.h"
 #include "base/logging.h"
 #include "content/public/renderer/media_stream_audio_sink.h"
 #include "third_party/webrtc/api/mediastreaminterface.h"
@@ -115,12 +117,24 @@ class MediaStreamRemoteAudioSource::AudioSink
 MediaStreamRemoteAudioTrack::MediaStreamRemoteAudioTrack(
     const blink::WebMediaStreamSource& source, bool enabled)
     : MediaStreamAudioTrack(false), source_(source), enabled_(enabled) {
-  DCHECK(source.extraData());  // Make sure the source has a native source.
+  DCHECK(source.extraData());
+
+  // Stop means that a track should be stopped permanently. But
+  // since there is no proper way of doing that on a remote track, we can
+  // at least disable the track. Blink will not call down to the content layer
+  // after a track has been stopped.
+  MediaStreamAudioTrack::AddStopObserver(base::Bind(
+      &MediaStreamRemoteAudioTrack::SetEnabled, base::Unretained(this), false));
 }
 
 MediaStreamRemoteAudioTrack::~MediaStreamRemoteAudioTrack() {
   DCHECK(main_render_thread_checker_.CalledOnValidThread());
   source()->RemoveAll(this);
+
+  // Even though the base class calls Stop(), do it here because the stop
+  // callback added in this class's constructor needs to be run before the data
+  // members of this class are destroyed.
+  Stop();
 }
 
 void MediaStreamRemoteAudioTrack::SetEnabled(bool enabled) {
@@ -139,15 +153,6 @@ void MediaStreamRemoteAudioTrack::SetEnabled(bool enabled) {
   source()->SetSinksEnabled(this, enabled);
 }
 
-void MediaStreamRemoteAudioTrack::Stop() {
-  DCHECK(main_render_thread_checker_.CalledOnValidThread());
-  // Stop means that a track should be stopped permanently. But
-  // since there is no proper way of doing that on a remote track, we can
-  // at least disable the track. Blink will not call down to the content layer
-  // after a track has been stopped.
-  SetEnabled(false);
-}
-
 void MediaStreamRemoteAudioTrack::AddSink(MediaStreamAudioSink* sink) {
   DCHECK(main_render_thread_checker_.CalledOnValidThread());
   return source()->AddSink(sink, this, enabled_);