MediaStream audio object graph untangling and clean-ups.

content/renderer/media/media_stream_audio_track.h

 // Copyright 2015 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.
 
 #ifndef CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_TRACK_H_
 #define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_TRACK_H_
 
+#include "base/callback.h"
 #include "base/macros.h"
 #include "content/renderer/media/media_stream_track.h"
 
 namespace webrtc {
 class AudioTrackInterface;
 }  // namespace webrtc
 
 namespace content {
 
 class MediaStreamAudioSink;
 
+// TODO(miu): In a soon-upcoming set of refactoring changes, this class will
+// take on the functionality of managing sink connections and the audio data
+// flow between source and sinks.  The WebRTC-specific elements will then be
+// moved into a subclass.   http://crbug.com/577874
 class CONTENT_EXPORT MediaStreamAudioTrack : public MediaStreamTrack {
  public:
   explicit MediaStreamAudioTrack(bool is_local_track);
+
+  // Subclasses must ensure the track is stopped (i.e., Stop() has been called
+  // at least once) before this destructor is invoked.
   ~MediaStreamAudioTrack() override;
 
-  static MediaStreamAudioTrack* GetTrack(
-      const blink::WebMediaStreamTrack& track);
+  // Returns the MediaStreamAudioTrack instance owned by the given blink |track|
+  // or null.
+  static MediaStreamAudioTrack* From(const blink::WebMediaStreamTrack& track);
 
   // Add a sink to the track. This function will trigger a OnSetFormat()
   // call on the |sink|.
   // Called on the main render thread.
   virtual void AddSink(MediaStreamAudioSink* sink) = 0;
 
   // Remove a sink from the track.
   // Called on the main render thread.
   virtual void RemoveSink(MediaStreamAudioSink* sink) = 0;
 
   // TODO(tommi, xians): Remove this method.
+  // TODO(miu): See class-level TODO comment.  ;-)
   virtual webrtc::AudioTrackInterface* GetAudioAdapter();
 
   // Returns the output format of the capture source. May return an invalid
   // AudioParameters if the format is not yet available.
   // Called on the main render thread.
   // TODO(tommi): This method appears to only be used by Pepper and in fact
   // does not appear to be necessary there.  We should remove it since it adds
   // to the complexity of all types of audio tracks+source implementations.
   virtual media::AudioParameters GetOutputFormat() const = 0;
 
+  // Called to notify this track that the flow of audio data has started from
+  // the source.  |stop_callback| is run by Stop() when the source must halt the
+  // flow of audio data to this track.
+  void Start(const base::Closure& stop_callback);
+
+  // Halts the flow of audio data from the source (and to the sinks), and then
+  // invokes OnStop() to perform any additional actions.
+  void Stop() final;
+
+ protected:
+  // Called by Stop() after the source has halted the flow of audio data.
+  virtual void OnStop();
+
  private:
+  // Callback provided to Start() which is run when the audio flow must halt.
+  base::Closure stop_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(MediaStreamAudioTrack);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_TRACK_H_