Add HostObserverInterface and decouple HeartbeatSender and ChromotingHost.

remoting/remoting.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
 
   'target_defaults': {
@@ skipping 210 matching lines @@
         'host/event_executor.h',
         'host/event_executor_linux.cc',
         'host/event_executor_mac.cc',
         'host/event_executor_win.cc',
         'host/heartbeat_sender.cc',
         'host/heartbeat_sender.h',
         'host/host_config.cc',
         'host/host_config.h',
         'host/host_key_pair.cc',
         'host/host_key_pair.h',
+        'host/host_status_observer.h',
         'host/in_memory_host_config.cc',
         'host/in_memory_host_config.h',
         'host/json_host_config.cc',
         'host/json_host_config.h',
         'host/screen_recorder.cc',
         'host/screen_recorder.h',
         'host/user_authenticator.h',
         'host/user_authenticator_linux.cc',
         'host/user_authenticator_mac.cc',
         'host/user_authenticator_win.cc',
@@ skipping 344 matching lines @@
       ],  # end of 'conditions'
     },  # end of target 'chromoting_unittests'
   ],  # end of targets
 }
 
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