Add the plumbing that will carry a clipboard item from a chromoting client to a host.

remoting/proto/internal.proto

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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;
 }
 
 // Defines an event message on the event channel.
 message EventMessage {
-  required int64 sequence_number = 1;  // Client timestamp for event
-  optional bool dummy = 2;       // Is this a dummy event?
+  required int64 sequence_number = 1;  // Client timestamp for event.
+  optional bool dummy = 2;       // Whether this is a dummy event.
 
   optional KeyEvent key_event = 3;
   optional MouseEvent mouse_event = 4;
 }