Add PluginMessageLoopProxy and use it for Host plugin UI thread.

remoting/host/chromoting_host.h

 // Copyright (c) 2011 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.
 
 #ifndef REMOTING_CHROMOTING_HOST_H_
 #define REMOTING_CHROMOTING_HOST_H_
 
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
 #include "base/threading/thread.h"
 #include "remoting/base/encoder.h"
+#include "remoting/base/plugin_message_loop_proxy.h"
 #include "remoting/host/access_verifier.h"
 #include "remoting/host/capturer.h"
 #include "remoting/host/client_session.h"
 #include "remoting/host/desktop_environment.h"
 #include "remoting/host/host_status_observer.h"
 #include "remoting/jingle_glue/jingle_thread.h"
 #include "remoting/jingle_glue/signal_strategy.h"
 #include "remoting/protocol/session_manager.h"
 #include "remoting/protocol/connection_to_client.h"
 
@@ skipping 206 matching lines @@
   // Stores list of tasks that should be executed when we finish
   // shutdown. Used only while |state_| is set to kStopping.
   std::vector<Task*> shutdown_tasks_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromotingHost);
 };
 
 }  // namespace remoting
 
 #endif  // REMOTING_HOST_CHROMOTING_HOST_H_