Cast: deliver video frames on the IO thread

content/renderer/media/media_stream_video_track.h

 // Copyright 2013 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_VIDEO_TRACK_H_
 #define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_VIDEO_TRACK_H_
 
 #include <vector>
 
 #include "base/compiler_specific.h"
+#include "base/gtest_prod_util.h"
 #include "base/memory/scoped_vector.h"
 #include "base/threading/thread_checker.h"
 #include "content/common/content_export.h"
 #include "content/public/renderer/media_stream_video_sink.h"
 #include "content/renderer/media/media_stream_track.h"
 #include "content/renderer/media/media_stream_video_source.h"
 
 namespace content {
 
 // MediaStreamVideoTrack is a video specific representation of a
@@ skipping 20 matching lines @@
       const blink::WebMediaStreamTrack& track);
 
   // Constructor for local video tracks.
    MediaStreamVideoTrack(
        MediaStreamVideoSource* source,
        const blink::WebMediaConstraints& constraints,
        const MediaStreamVideoSource::ConstraintsCallback& callback,
        bool enabled);
   virtual ~MediaStreamVideoTrack();
 
-  // Add |sink| to receive state changes and video frames on the main render
-  // thread.
-  virtual void AddSink(MediaStreamVideoSink* sink);
-  virtual void RemoveSink(MediaStreamVideoSink* sink);
-
-  // Add |sink| to receive state changes on the main render thread and video
-  // frames in the |callback| method on the IO-thread.
-  virtual void AddSink(MediaStreamSink* sink,
-                       const VideoCaptureDeliverFrameCB& callback);
-  virtual void RemoveSink(MediaStreamSink* sink);
-
   virtual void SetEnabled(bool enabled) OVERRIDE;
   virtual void Stop() OVERRIDE;
 
   void OnReadyStateChanged(blink::WebMediaStreamSource::ReadyState state);
 
   const blink::WebMediaConstraints& constraints() const {
     return constraints_;
   }
 
  protected:
   // Used to DCHECK that we are called on the correct thread.
   base::ThreadChecker thread_checker_;
 
  private:
+  // MediaStreamVideoSink is a friend to allow it to call AddSink() and
+  // RemoveSink().
+  friend class MediaStreamVideoSink;
+  FRIEND_TEST_ALL_PREFIXES(MediaStreamRemoteVideoSourceTest, StartTrack);
+  FRIEND_TEST_ALL_PREFIXES(MediaStreamRemoteVideoSourceTest, RemoteTrackStop);
+  FRIEND_TEST_ALL_PREFIXES(VideoDestinationHandlerTest, PutFrame);
+
+  // Add |sink| to receive state changes on the main render thread and video
+  // frames in the |callback| method on the IO-thread.
+  // |callback| will be reset on the render thread.
+  // These two methods are private such that no subclass can intercept and
+  // store the callback. This is important to ensure that we can release
+  // the callback on render thread without reference to it on the IO-thread.
+  void AddSink(MediaStreamVideoSink* sink,
+               const VideoCaptureDeliverFrameCB& callback);
+  void RemoveSink(MediaStreamVideoSink* sink);
+
   // |FrameDeliverer| is an internal helper object used for delivering video
   // frames on the IO-thread using callbacks to all registered tracks.
   class FrameDeliverer;
   scoped_refptr<FrameDeliverer> frame_deliverer_;
 
   blink::WebMediaConstraints constraints_;
 
   // Weak ref to the source this tracks is connected to.  |source_| is owned
   // by the blink::WebMediaStreamSource and is guaranteed to outlive the
   // track.
   MediaStreamVideoSource* source_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaStreamVideoTrack);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_VIDEO_TRACK_H_