Add logging statements to places where the frame might be dropped in WebRTC pipeline.

webrtc/media/base/videobroadcaster.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 33 matching lines @@
   return !sink_pairs().empty();
 }
 
 VideoSinkWants VideoBroadcaster::wants() const {
   rtc::CritScope cs(&sinks_and_wants_lock_);
   return current_wants_;
 }
 
 void VideoBroadcaster::OnFrame(const cricket::VideoFrame& frame) {
   rtc::CritScope cs(&sinks_and_wants_lock_);
+  if (sink_pairs().empty())
+    LOG(LS_INFO) << "Dropping frame because there are no sink pairs in video "

[perkj_webrtc, 2016/09/26 06:46:34]

This may soon start spitting out logs in chrome that would be hit when a
PeerConnection is created  but negotiation is not complete. I think it would be
better if you instead add logs where a sink is added to a source in the source
subclasses. If you do it here you will not know if it is a local or remote
source.

[sakal, 2016/09/26 11:23:59]

I changed it to log VideoBroadcaster creation and adding a sink. Idea being that
if a video broadcaster is created but a sink is never added we should look into
it.

I tried adding logging to places where AddOrUpdateSink is called but it seems
like a lot of work to trace where the calls are actually coming from.

[magjed_webrtc, 2016/09/27 15:06:11]

It's probably good to have logs for VideoBroadcaster creation and adding a sink
regardless, but can't we keep this log? It's so much more explicit and obvious
if we see this log in bugreports instead of trying to track down when and how
sinks are added. Also logs are sometimes cropped, so it might not even be
possible. I don't think Chrome will spit out this log since local video is shown
before negotiation is complete, and is it really a problem if we get a few of
these logs in fringe cases? We know from the context in bugreports if local or
remote video is missing, so that's not a problem.

+                    "broadcaster.";
   for (auto& sink_pair : sink_pairs()) {
     if (sink_pair.wants.rotation_applied &&
         frame.rotation() != webrtc::kVideoRotation_0) {
       // Calls to OnFrame are not synchronized with changes to the sink wants.
       // When rotation_applied is set to true, one or a few frames may get here
       // with rotation still pending. Protect sinks that don't expect any
       // pending rotation.
       LOG(LS_VERBOSE) << "Discarding frame with unexpected rotation.";
       continue;
     }
@@ skipping 46 matching lines @@
     rtc::scoped_refptr<webrtc::I420Buffer> buffer =
         new RefCountedObject<webrtc::I420Buffer>(width, height);
     buffer->SetToBlack();
     black_frame_buffer_ = buffer;
   }
 
   return black_frame_buffer_;
 }
 
 }  // namespace rtc