Created multi-process-friendly PowerMonitor interface.

content/common/power_monitor_client.h

+// 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 CONTENT_COMMON_POWER_MONITOR_CLIENT_H_
+#define CONTENT_COMMON_POWER_MONITOR_CLIENT_H_
+
+#include "base/basictypes.h"
+#include "base/observer_list_threadsafe.h"
+#include "base/power_monitor/power_observer.h"
+
+#include "content/common/content_export.h"
+
+namespace content {
+
+// A class used to monitor the power state change and notify the observers about
+// the change event.
+class CONTENT_EXPORT PowerMonitorClient {

[wrong vandebo, 2013/06/24 16:34:49]

So this class looks basically the same as base::SysteMonitor.  Why not just
reuse/extend that? One way would be to change base::SystemMonitor to have a
constructor that takes a SystemMonitorSource thing and then
PowerMonitorMessageFilter can be an implementation of that.

[bajones, 2013/06/25 18:33:34]

I assume you mean base::PowerMonitor, not base::SystemMonitor (which doesn't
look related)? If so then yes, that sounds like a great idea!

[vandebo (ex-Chrome), 2013/06/25 18:37:14]

Oops, yes, base::PowerMonitor  (PowerMonitor was extract from SystemMonitor
fairly recently.)

+public:
+  PowerMonitorClient();

[Ken Russell (switch to Gerrit), 2013/06/24 22:54:38]

Since this class is a singleton the constructor and destructor should be
private, and the sole instance only available via PowerMonitorClient::Get().

[bajones, 2013/06/25 18:33:34]

That would be my thinking as well, but that's not how the existing PowerMonitor
(which this is modeled after) instances work.

+  ~PowerMonitorClient();
+
+  // Get the process-wide PowerMonitorClient (if not present, returns NULL).
+  static PowerMonitorClient* Get();
+
+  // Add and remove an observer.
+  // Can be called from any thread.
+  // Must not be called from within a notification callback.
+  void AddObserver(base::PowerObserver* observer);
+  void RemoveObserver(base::PowerObserver* observer);
+
+  // Is the computer currently on battery power. Can be called on any thread.
+  bool BatteryPower() const {
+    // Using a lock here is not necessary for just a bool.

[scottmg, 2013/06/22 00:11:24]

tsan will not agree

+    return battery_in_use_;
+  }
+
+private:
+  friend class PowerMonitorMessageFilter;
+
+  void NotifyPowerStateChange(bool battery_in_use);
+  void NotifySuspend();
+  void NotifyResume();
+
+  scoped_refptr<ObserverListThreadSafe<base::PowerObserver> > observers_;
+  bool battery_in_use_;
+
+  DISALLOW_COPY_AND_ASSIGN(PowerMonitorClient);
+};
+
+}  // namespace base
+
+#endif  // CONTENT_COMMON_POWER_MONITOR_CLIENT_H_