SystemMonitor refactoring: move power state monitor into a separate class called PowerMonitor

base/power_monitor/power_observer.h

-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Copyright 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 BASE_DEFAULT_CLOCK_H_
-#define BASE_DEFAULT_CLOCK_H_
+#ifndef BASE_POWER_MONITOR_POWER_OBSERVER_H_
+#define BASE_POWER_MONITOR_POWER_OBSERVER_H_
 
 #include "base/base_export.h"
 #include "base/compiler_specific.h"
-#include "base/time/clock.h"
 
 namespace base {
 
-// DefaultClock is a Clock implementation that uses Time::Now().
-class BASE_EXPORT DefaultClock : public Clock {
+class BASE_EXPORT PowerObserver {
  public:
-  virtual ~DefaultClock();
+  // Notification of a change in power status of the computer, such
+  // as from switching between battery and A/C power.
+  virtual void OnPowerStateChange(bool on_battery_power) {};
 
-  // Simply returns Time::Now().
-  virtual Time Now() OVERRIDE;
+  // Notification that the system is suspending.
+  virtual void OnSuspend() {}
+
+  // Notification that the system is resuming.
+  virtual void OnResume() {}
+
+ protected:
+  virtual ~PowerObserver() {}
 };
 
 }  // namespace base
 
-#endif  // BASE_DEFAULT_CLOCK_H_
+#endif  // BASE_POWER_MONITOR_POWER_OBSERVER_H_