Created multi-process-friendly PowerMonitor interface.

base/power_monitor/power_monitor_source.h

Index: base/power_monitor/power_monitor_source.h
diff --git a/base/power_monitor/power_monitor_source.h b/base/power_monitor/power_monitor_source.h
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+++ b/base/power_monitor/power_monitor_source.h
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+// 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_POWER_MONITOR_POWER_MONITOR_SOURCE_H_
+#define BASE_POWER_MONITOR_POWER_MONITOR_SOURCE_H_
+
+#include "base/base_export.h"
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/observer_list_threadsafe.h"
+#include "base/synchronization/lock.h"
+
+namespace base {
+
+class PowerMonitor;
+
+// Communicates power state changes to the power monitor.
+class BASE_EXPORT PowerMonitorSource {
+ public:
+  PowerMonitorSource();
+  virtual ~PowerMonitorSource();
+
+  // Normalized list of power events.
+  enum PowerEvent {
+    POWER_STATE_EVENT,  // The Power status of the system has changed.
+    SUSPEND_EVENT,      // The system is being suspended.
+    RESUME_EVENT        // The system is being resumed.
+  };
+
+  // Is the computer currently on battery power. Can be called on any thread.
+  bool IsOnBatteryPower();
+
+ protected:
+  friend class PowerMonitorTest;
+
+  // Friend function that is allowed to access the protected ProcessPowerEvent.
+  friend void ProcessPowerEventHelper(PowerEvent);
+
+  // Get the process-wide PowerMonitorSource (if not present, returns NULL).
+  static PowerMonitorSource* Get();
+
+  static void ProcessPowerEvent(PowerEvent event_id);
+
+  // Updates the cached battery power state. Returns true if state has changed.
+  bool UpdateOnBatteryPower();
+
+  // Platform-specific method to check whether the system is currently
+  // running on battery power.  Returns true if running on batteries,
+  // false otherwise.
+  virtual bool IsOnBatteryPowerImpl() = 0;
+
+ private:
+  bool on_battery_power_;
+  bool suspended_;
+  Lock lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(PowerMonitorSource);
+};
+
+}  // namespace base
+
+#endif  // BASE_POWER_MONITOR_POWER_MONITOR_SOURCE_H_