Added JsonMessage to the control channel.

remoting/host/client_session.cc

Index: remoting/host/client_session.cc
diff --git a/remoting/host/client_session.cc b/remoting/host/client_session.cc
index 86bbe7ffa12800eb0bcb1f213f888acc2e28cdd2..b1bc7d1ebc3f9372e9f1186961d31a2df91a1f39 100644
--- a/remoting/host/client_session.cc
+++ b/remoting/host/client_session.cc
@@ -187,6 +187,12 @@ void ClientSession::RequestPairing(
   }
 }
 
+void ClientSession::ProcessClientJson(const protocol::JsonMessage& message) {
+  // No messages are currently supported.
+  LOG(INFO) << "Unexpected message received: "
+            << message.type() << ": " << message.json();
+}
+
 void ClientSession::OnConnectionAuthenticated(
     protocol::ConnectionToClient* connection) {
   DCHECK(CalledOnValidThread());