Adding logs to track potential cause of not starting port allocation.

webrtc/p2p/base/transportcontroller.cc

Index: webrtc/p2p/base/transportcontroller.cc
diff --git a/webrtc/p2p/base/transportcontroller.cc b/webrtc/p2p/base/transportcontroller.cc
index de98df23bc51c17319f398288576eaa86e5b6131..e6182bdef037019931d6d4991c1d8b3fd677d142 100644
--- a/webrtc/p2p/base/transportcontroller.cc
+++ b/webrtc/p2p/base/transportcontroller.cc
@@ -455,6 +455,12 @@ bool TransportController::SetLocalTransportDescription_n(
     // it could have been deleted as a result of bundling.
     // TODO(deadbeef): Make callers smarter so they won't attempt to set a
     // description on a deleted transport.
+    // This assumes we always bundle all media on the audio transport, so I
+    // only log a message here.
+    if (transport_name == CN_AUDIO) {

[pthatcher1, 2016/09/08 17:55:27]

We don't always bundle on audio, and this would log an error for every single
PeerConnection that uses only data channels. 

You might be better off logging all transports that are in the
TransportController after every call to PeerConnecction::SetLocalDescription.

[honghaiz3, 2016/09/08 21:30:11]

If we are using data-channel only, then the transport should not have been
deleted due to bundle (so transport should not be nullptr), right?

+      LOG(LS_ERROR) << "No transport is found for audio when setting "
+                    << "local transport description";
+    }
     return true;
   }