Add HostObserverInterface and decouple HeartbeatSender and ChromotingHost.

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 "base/memory/ref_counted.h"
+
+namespace remoting {
+
+class SignalStrategy;
+
+class HostStatusObserver
+    : public base::RefCountedThreadSafe<HostStatusObserver> {
+ public:
+  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 main thread when the host shuts down.
+  virtual void OnShutdown() = 0;
+
+ protected:
+  friend class base::RefCountedThreadSafe<HostStatusObserver>;
+  virtual ~HostStatusObserver() { }
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_HOST_STATUS_OBSERVER_H_