Refactor VideoTracks to forward all sinks to its source

webrtc/media/base/videobroadcaster.cc

Index: webrtc/media/base/videobroadcaster.cc
diff --git a/webrtc/media/base/videobroadcaster.cc b/webrtc/media/base/videobroadcaster.cc
index 015f5206b676e239666e4fa5f374ebecb2a0270c..ed1a826de0323a0d9b6c2c30c40b58da19b42d7f 100644
--- a/webrtc/media/base/videobroadcaster.cc
+++ b/webrtc/media/base/videobroadcaster.cc
@@ -65,7 +65,11 @@ VideoSinkWants VideoBroadcaster::wants() const {
 void VideoBroadcaster::OnFrame(const cricket::VideoFrame& frame) {
   rtc::CritScope cs(&sinks_and_wants_lock_);
   for (auto& sink_pair : sinks_) {
-    sink_pair.sink->OnFrame(frame);
+    if (sink_pair.wants.black_frames) {
+      sink_pair.sink->OnFrame(GetBlackFrame(frame));
+    } else {
+      sink_pair.sink->OnFrame(frame);
+    }
   }
 }
 
@@ -112,4 +116,21 @@ void VideoBroadcaster::UpdateWants() {
   current_wants_ = wants;
 }
 
+const cricket::VideoFrame& VideoBroadcaster::GetBlackFrame(
+    const cricket::VideoFrame& frame) {
+  if (black_frame_ && black_frame_->GetWidth() == frame.GetWidth() &&
+      black_frame_->GetHeight() == frame.GetHeight() &&
+      black_frame_->GetVideoRotation() == frame.GetVideoRotation()) {
+    black_frame_->SetTimeStamp(frame.GetTimeStamp());
+    return *black_frame_;
+  }
+  black_frame_.reset(new cricket::WebRtcVideoFrame(
+      new rtc::RefCountedObject<webrtc::I420Buffer>(
+          static_cast<int>(frame.GetWidth()),
+          static_cast<int>(frame.GetHeight())),
+      frame.GetTimeStamp(), frame.GetVideoRotation()));
+  black_frame_->SetToBlack();
+  return *black_frame_;
+}
+
 }  // namespace rtc