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
new file mode 100644
index 0000000000000000000000000000000000000000..da643c0d8502f69d2bbd1d152e4897e4cbd7b3b8
--- /dev/null
+++ b/base/power_monitor/power_monitor_source.h
@@ -0,0 +1,62 @@
+// 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();
+
+  // ProcessPowerEvent should only be called from a single thread, most likely
+  // the UI thread or, in child processes, the IO thread.

[piman, 2013/07/15 20:51:30]

With your changes, it is now called on the main thread, which is also the thread
it gets created on. Do you still need the lock?

[bajones, 2013/07/15 22:27:18]

The lock is for IsOnBatteryPower(), which (as the comment says) can be called on
any thread. This was behavior that was documented via comment (but not enforced
by the code!) prior to this patch and thus I'm trying to preserve it.
Documentation has been added and the name changed for clarity.

+  static void ProcessPowerEvent(PowerEvent event_id);
+
+  // 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_