Add a 'remote' property to MediaSourceInterface. Also adding an implementation to the relevant sour…

talk/app/webrtc/rtpreceiver.cc

Index: talk/app/webrtc/rtpreceiver.cc
diff --git a/talk/app/webrtc/rtpreceiver.cc b/talk/app/webrtc/rtpreceiver.cc
index b88554f0ac4d5f6f1108adf042c7284820914ef4..2b3505344669c2a07460915600868a7930e0ffa2 100644
--- a/talk/app/webrtc/rtpreceiver.cc
+++ b/talk/app/webrtc/rtpreceiver.cc
@@ -85,6 +85,7 @@ VideoRtpReceiver::VideoRtpReceiver(VideoTrackInterface* track,
                                    uint32_t ssrc,
                                    VideoProviderInterface* provider)
     : id_(track->id()), track_(track), ssrc_(ssrc), provider_(provider) {
+  RTC_DCHECK(track_->GetSource()->remote());
   provider_->SetVideoPlayout(ssrc_, true, track_->GetSource()->FrameInput());
 }