Propagate connection state from networking layer to UI.

remoting/protocol/session.h

Index: remoting/protocol/session.h
diff --git a/remoting/protocol/session.h b/remoting/protocol/session.h
index 3137c3ea6307ec513b12f74756ba20f1d1970290..91483187d341faa7cabbb1c5056c4f6ede429fb1 100644
--- a/remoting/protocol/session.h
+++ b/remoting/protocol/session.h
@@ -66,6 +66,12 @@ class Session : public base::NonThreadSafe {
     // handler of this event.
     virtual void OnSessionRouteChange(const std::string& channel_name,
                                       const TransportRoute& route) = 0;
+
+    // Called when ready state on one of the channels changes. See
+    // comments in transport.h for explanation on what this state
+    // means and how it can used.
+    virtual void OnSessionChannelReady(const std::string& channel_name,
+                                       bool ready) {}
   };
 
   // TODO(sergeyu): Specify connection error code when channel