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

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 d3bc7a09cebccdcfccb839cda8e1dcd6d8aeadb7..4276984494ae224f454e7ef9b7da7c9f1ee94b62 100644
--- a/webrtc/media/base/videobroadcaster.cc
+++ b/webrtc/media/base/videobroadcaster.cc
@@ -51,6 +51,9 @@ VideoSinkWants VideoBroadcaster::wants() const {
 
 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) {