Replace SetCapturer and SetCaptureDevice by SetSource.

webrtc/api/videotrack.cc

Index: webrtc/api/videotrack.cc
diff --git a/webrtc/api/videotrack.cc b/webrtc/api/videotrack.cc
index bd380254b2d0e5ab7ab961152799b9ba4c33af16..c1858d8399bc05e11b3b16789456cf71be0481e3 100644
--- a/webrtc/api/videotrack.cc
+++ b/webrtc/api/videotrack.cc
@@ -31,10 +31,12 @@ std::string VideoTrack::kind() const {
   return kVideoKind;
 }
 
+// AddOrUpdateSink and RemoveSink should be called on the worker
+// thread.
 void VideoTrack::AddOrUpdateSink(
     rtc::VideoSinkInterface<cricket::VideoFrame>* sink,
     const rtc::VideoSinkWants& wants) {
-  RTC_DCHECK(thread_checker_.CalledOnValidThread());
+  // RTC_DCHECK(thread_checker_.CalledOnValidThread());
   VideoSourceBase::AddOrUpdateSink(sink, wants);
   rtc::VideoSinkWants modified_wants = wants;
   modified_wants.black_frames = !enabled();
@@ -43,7 +45,7 @@ void VideoTrack::AddOrUpdateSink(
 
 void VideoTrack::RemoveSink(
     rtc::VideoSinkInterface<cricket::VideoFrame>* sink) {
-  RTC_DCHECK(thread_checker_.CalledOnValidThread());
+  // RTC_DCHECK(thread_checker_.CalledOnValidThread());
   VideoSourceBase::RemoveSink(sink);
   video_source_->RemoveSink(sink);
 }
@@ -53,6 +55,8 @@ bool VideoTrack::set_enabled(bool enable) {
   for (auto& sink_pair : sink_pairs()) {
     rtc::VideoSinkWants modified_wants = sink_pair.wants;
     modified_wants.black_frames = !enable;
+    // video_source_ is a proxy object, marshalling the call to the
+    // worker thread.
     video_source_->AddOrUpdateSink(sink_pair.sink, modified_wants);
   }
   return MediaStreamTrack<VideoTrackInterface>::set_enabled(enable);