Cast: deliver video frames on the IO thread

content/renderer/media/video_frame_deliverer.h

 // 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.
 
 #ifndef CONTENT_RENDERER_MEDIA_VIDEO_FRAME_DELIVERER_H_
 #define CONTENT_RENDERER_MEDIA_VIDEO_FRAME_DELIVERER_H_
 
 #include <utility>
 #include <vector>
 
@@ skipping 12 matching lines @@
 // Its used by MediaStreamVideoTrack and MediaStreamVideoSource.
 class VideoFrameDeliverer
     : public base::RefCountedThreadSafe<VideoFrameDeliverer> {
  public:
   explicit VideoFrameDeliverer(
       const scoped_refptr<base::MessageLoopProxy>& io_message_loop);
 
   // Add |callback| to receive video frames on the IO-thread.
   // Must be called on the main render thread.
   void AddCallback(void* id, const VideoCaptureDeliverFrameCB& callback);
+
   // Removes |callback| associated with |id| from receiving video frames if |id|
   // has been added. It is ok to call RemoveCallback even if the |id| has not
-  // been added.
+  // been added. Note that the added callback will be reset on the main thread.
   // Must be called on the main render thread.
   void RemoveCallback(void* id);
 
   // Triggers all registered callbacks with |frame| and |format| as parameters.
   // Must be called on the IO-thread.
   virtual void DeliverFrameOnIO(
       const scoped_refptr<media::VideoFrame>& frame,
       const media::VideoCaptureFormat& format);
 
   const scoped_refptr<base::MessageLoopProxy>& io_message_loop() const {
     return io_message_loop_;
   }
 
  protected:
   void AddCallbackOnIO(void* id, const VideoCaptureDeliverFrameCB& callback);
+
+  // Callback will be removed and then reset on the designated message loop.
   // It is ok to call RemoveCallback even if |id| has not been added.
-  void RemoveCallbackOnIO(void* id);
+  void RemoveCallbackOnIO(
+      void* id, const scoped_refptr<base::MessageLoopProxy>& message_loop);
 
  protected:
   virtual ~VideoFrameDeliverer();
   const base::ThreadChecker& thread_checker() const {
     return thread_checker_;
   }
 
  private:
   friend class base::RefCountedThreadSafe<VideoFrameDeliverer>;
 
   // Used to DCHECK that AddCallback and RemoveCallback are called on the main
   // render thread.
   base::ThreadChecker thread_checker_;
   scoped_refptr<base::MessageLoopProxy> io_message_loop_;
 
   typedef std::pair<void*, VideoCaptureDeliverFrameCB> VideoIdCallbackPair;
   std::vector<VideoIdCallbackPair> callbacks_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoFrameDeliverer);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_VIDEO_FRAME_DELIVERER_H_