Refactor VideoTracks to forward all sinks to its source

webrtc/media/base/videobroadcaster.h

Index: webrtc/media/base/videobroadcaster.h
diff --git a/webrtc/media/base/videobroadcaster.h b/webrtc/media/base/videobroadcaster.h
index b4227eaba6f314fe65f73492be7ae5d1b43ea4c8..7e76752d0982bcaf9a016586ee9b7ec827dc191b 100644
--- a/webrtc/media/base/videobroadcaster.h
+++ b/webrtc/media/base/videobroadcaster.h
@@ -19,6 +19,7 @@
 #include "webrtc/media/base/videoframe.h"
 #include "webrtc/media/base/videosinkinterface.h"
 #include "webrtc/media/base/videosourceinterface.h"
+#include "webrtc/media/engine/webrtcvideoframe.h"
 
 namespace rtc {
 
@@ -56,12 +57,16 @@ class VideoBroadcaster : public VideoSourceInterface<cricket::VideoFrame>,
   SinkPair* FindSinkPair(const VideoSinkInterface<cricket::VideoFrame>* sink)
       EXCLUSIVE_LOCKS_REQUIRED(sinks_and_wants_lock_);
   void UpdateWants() EXCLUSIVE_LOCKS_REQUIRED(sinks_and_wants_lock_);
+  const cricket::VideoFrame& GetBlackFrame(const cricket::VideoFrame& frame)
+      EXCLUSIVE_LOCKS_REQUIRED(sinks_and_wants_lock_);
 
   ThreadChecker thread_checker_;
   rtc::CriticalSection sinks_and_wants_lock_;
 
   VideoSinkWants current_wants_ GUARDED_BY(sinks_and_wants_lock_);
   std::vector<SinkPair> sinks_ GUARDED_BY(sinks_and_wants_lock_);
+
+  rtc::scoped_ptr<cricket::WebRtcVideoFrame> black_frame_;
 };
 
 }  // namespace rtc