Extended proxy abstraction, to call certain methods to the worker thread.

webrtc/api/rtpreceiver.cc

Index: webrtc/api/rtpreceiver.cc
diff --git a/webrtc/api/rtpreceiver.cc b/webrtc/api/rtpreceiver.cc
index 0150dfd546c25e3b238b61a22e8ed58adf7dbd0d..422255225a1131deec08cb5c4b8f681a5a034373 100644
--- a/webrtc/api/rtpreceiver.cc
+++ b/webrtc/api/rtpreceiver.cc
@@ -85,6 +85,7 @@ VideoRtpReceiver::VideoRtpReceiver(MediaStreamInterface* stream,
                                                      true /* remote */)),
       track_(VideoTrackProxy::Create(
           rtc::Thread::Current(),
+          worker_thread,
           VideoTrack::Create(track_id, source_.get()))) {
   source_->SetState(MediaSourceInterface::kLive);
   provider_->SetVideoPlayout(ssrc_, true, &broadcaster_);