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

remoting/proto/internal.proto

Index: remoting/proto/internal.proto
diff --git a/remoting/proto/internal.proto b/remoting/proto/internal.proto
index e63982d9b450359fb733ab7b9dc9f3f7da2d5b2a..1965b823309222874cf3bd731984df558ca89b96 100644
--- a/remoting/proto/internal.proto
+++ b/remoting/proto/internal.proto
@@ -1,4 +1,4 @@
-// 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.
 
@@ -20,9 +20,10 @@ message ControlMessage {
 
 // 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;
+  optional ClipboardEvent clipboard_event = 5;
 }