Split host plugin into multiple files.

remoting/host/host_status_observer.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_HOST_STATUS_OBSERVER_H_
 #define REMOTING_HOST_STATUS_OBSERVER_H_
 
+#include <string>
+
 namespace remoting {
 
 class SignalStrategy;
 
 class HostStatusObserver {
  public:
   HostStatusObserver() { }
   virtual ~HostStatusObserver() { }
 
   // Called on the network thread when status of the XMPP changes.
   virtual void OnSignallingConnected(SignalStrategy* signal_strategy,
                                      const std::string& full_jid) = 0;
   virtual void OnSignallingDisconnected() = 0;
 
   // Called on the network thread when an unauthorized user attempts
   // to connect to the host.
   virtual void OnAccessDenied() = 0;
 
   // Called on the main thread when the host shuts down.
   virtual void OnShutdown() = 0;
 };
 
 }  // namespace remoting
 
 #endif  // REMOTING_HOST_STATUS_OBSERVER_H_