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.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_POWER_MONITOR_POWER_OBSERVER_H_
+#define BASE_POWER_MONITOR_POWER_OBSERVER_H_
+
+#include "base/base_export.h"
+#include "base/compiler_specific.h"
+
+namespace base {
+
+// Callbacks will be called on the thread which creates the PowerMonitor.
+// During the callback, Add/RemoveObserver will block until the callbacks
+// are finished. Observers should implement quick callback functions; if
+// lengthy operations are needed, the observer should take care to invoke
+// the operation on an appropriate thread.
+class BASE_EXPORT PowerObserver {
+ public:
+  // 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) {};
+
+  // 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_POWER_MONITOR_POWER_OBSERVER_H_