Add PeerConnection IsClosed check.

webrtc/api/webrtcsession.h

Index: webrtc/api/webrtcsession.h
diff --git a/webrtc/api/webrtcsession.h b/webrtc/api/webrtcsession.h
index 98217bff266a2a67e7fbb99964210051d88fa5a1..987f026655926d8ff9a1fe7abb9f94bb4bbd1364 100644
--- a/webrtc/api/webrtcsession.h
+++ b/webrtc/api/webrtcsession.h
@@ -321,6 +321,11 @@ class WebRtcSession : public AudioProviderInterface,
     metrics_observer_ = metrics_observer;
   }
 
+  // Set the transport controller and subscribe the Signals from the
+  // TransportController.
+  void SetTransportController(
+      cricket::TransportController* transport_controller);
+
   // Called when voice_channel_, video_channel_ and data_channel_ are created
   // and destroyed. As a result of, for example, setting a new description.
   sigslot::signal0<> SignalVoiceChannelCreated;