Hook up system clock update dbus signal to chrome and ash tray ui.

chromeos/dbus/system_clock_client.h

+// Copyright (c) 2013 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 CHROMEOS_DBUS_SYSTEM_CLOCK_CLIENT_H_
+#define CHROMEOS_DBUS_SYSTEM_CLOCK_CLIENT_H_
+
+#include "base/observer_list.h"
+#include "chromeos/chromeos_export.h"
+#include "chromeos/dbus/dbus_client_implementation_type.h"
+
+namespace dbus {
+class Bus;
+}  // namespace
+
+namespace chromeos {
+
+// SystemClockClient is used to communicate with the system clock.
+class CHROMEOS_EXPORT SystemClockClient {
+ public:
+  // Interface for observing changes from the system clock.
+  class Observer {
+   public:
+    // Called when the status is updated.
+    virtual void SystemClockUpdated() {}

[stevenjb, 2013/03/13 17:34:31]

Add:
 protected:
  virtual void ~Observer {}

(I know we don't do this everywhere, but we really should)

[jennyz, 2013/03/13 19:14:02]

Done.

+  };
+
+  virtual ~SystemClockClient();
+
+  // Adds and removes the observer.
+  virtual void AddObserver(Observer* observer) = 0;
+  virtual void RemoveObserver(Observer* observer) = 0;
+  // Returns true if this object has the given observer.
+  virtual bool HasObserver(Observer* observer) = 0;
+
+  // Creates the instance.
+  static SystemClockClient* Create(DBusClientImplementationType type,
+                                   dbus::Bus* bus);
+
+ protected:
+  // Create() should be used instead.
+  SystemClockClient();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SystemClockClient);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROMEOS_DBUS_SYSTEM_CLOCK_CLIENT_H_