MediaStream audio object graph untangling and clean-ups.

content/renderer/media/media_stream_audio_source.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_source.h"
 
 #include "content/renderer/render_frame_impl.h"
+#include "third_party/WebKit/public/platform/WebMediaStreamSource.h"
 
 namespace content {
 
 MediaStreamAudioSource::MediaStreamAudioSource(
     int render_frame_id,
     const StreamDeviceInfo& device_info,
     const SourceStoppedCallback& stop_callback,
     PeerConnectionDependencyFactory* factory)
     : render_frame_id_(render_frame_id), factory_(factory) {
   SetDeviceInfo(device_info);
   SetStopCallback(stop_callback);
 }
 
 MediaStreamAudioSource::MediaStreamAudioSource()
     : render_frame_id_(-1), factory_(NULL) {
 }
 
 MediaStreamAudioSource::~MediaStreamAudioSource() {}
 
+// static
+MediaStreamAudioSource* MediaStreamAudioSource::From(
+    const blink::WebMediaStreamSource& source) {
+  if (source.isNull() ||
+      source.type() != blink::WebMediaStreamSource::TypeAudio) {
+    return nullptr;
+  }
+  return static_cast<MediaStreamAudioSource*>(source.extraData());
+}
+
 void MediaStreamAudioSource::DoStopSource() {
   if (audio_capturer_.get())
     audio_capturer_->Stop();
 }
 
 void MediaStreamAudioSource::AddTrack(
     const blink::WebMediaStreamTrack& track,
     const blink::WebMediaConstraints& constraints,
     const ConstraintsCallback& callback) {
   // TODO(xians): Properly implement for audio sources.
   if (!local_audio_source_.get()) {
     if (!factory_->InitializeMediaStreamAudioSource(render_frame_id_,
                                                     constraints, this)) {
       // The source failed to start.
       // UserMediaClientImpl rely on the |stop_callback| to be triggered when
       // the last track is removed from the source. But in this case, the
       // source is is not even started. So we need to fail both adding the
       // track and trigger |stop_callback|.
       callback.Run(this, MEDIA_DEVICE_TRACK_START_FAILURE, "");
       StopSource();
       return;
     }
   }
 
   factory_->CreateLocalAudioTrack(track);
   callback.Run(this, MEDIA_DEVICE_OK, "");
 }
 
 }  // namespace content