Added JsonMessage to the control channel.

remoting/proto/internal.proto

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Internal message types that should not be seen outside the protocol
 // directory.
 
 syntax = "proto2";
 
 import "control.proto";
 import "event.proto";
 
 option optimize_for = LITE_RUNTIME;
 
 package remoting.protocol;
 
 // Represents a message being sent on the control channel.
 message ControlMessage {
   optional ClipboardEvent clipboard_event = 1;
   optional ClientResolution client_resolution = 2;
   optional CursorShapeInfo cursor_shape = 4;
   optional VideoControl video_control = 3;
   optional AudioControl audio_control = 5;
   optional Capabilities capabilities = 6;
   optional PairingRequest pairing_request = 7;
   optional PairingResponse pairing_response = 8;
+  optional ExtensionMessage extension_message = 9;
 }
 
 // Defines an event message on the event channel.
 message EventMessage {
   optional int64 sequence_number = 1;  // Client timestamp for event.
 
   optional KeyEvent key_event = 3;
   optional MouseEvent mouse_event = 4;
 }