Fix a breakage in chromoting due to an interface change.

TBR=pthatcher@webrtc.org

Review URL: https://codereview.webrtc.org/2091093002 .

Cr-Commit-Position: refs/heads/master@{#13276}

webrtc/p2p/base/p2ptransportchannel.h

@@ -118,6 +118,10 @@ class P2PTransportChannel : public TransportChannelImpl,
   int GetError() override { return error_; }
   bool GetStats(std::vector<ConnectionInfo>* stats) override;
 
+  // TODO(honghaiz): Remove this method once the reference of it in
+  // Chromoting is removed.
+  const Connection* best_connection() const { return selected_connection_; }
+
   const Connection* selected_connection() const { return selected_connection_; }
   void set_incoming_only(bool value) { incoming_only_ = value; }