Created multi-process-friendly PowerMonitor interface.

base/power_monitor/power_monitor_source.cc

Index: base/power_monitor/power_monitor_source.cc
diff --git a/base/power_monitor/power_monitor_source.cc b/base/power_monitor/power_monitor_source.cc
new file mode 100644
index 0000000000000000000000000000000000000000..2da38d2b4dce5b47eab748d649694177abff5d57
--- /dev/null
+++ b/base/power_monitor/power_monitor_source.cc
@@ -0,0 +1,60 @@
+// 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.
+
+#include "base/power_monitor/power_monitor_source.h"
+
+#include "base/power_monitor/power_monitor.h"
+
+namespace base {
+
+PowerMonitorSource::PowerMonitorSource()
+    : on_battery_power_(false),
+      suspended_(false) {
+}
+
+PowerMonitorSource::~PowerMonitorSource() {
+}
+
+bool PowerMonitorSource::IsOnBatteryPower() {
+  AutoLock auto_lock(lock_);
+  return on_battery_power_;
+}
+
+bool PowerMonitorSource::UpdateOnBatteryPower() {
+  AutoLock auto_lock(lock_);
+  bool old_on_battery_power = on_battery_power_;
+  on_battery_power_ = IsOnBatteryPowerImpl();
+  return old_on_battery_power != on_battery_power_;
+}
+
+void PowerMonitorSource::ProcessPowerEvent(PowerEvent event_id) {
+  PowerMonitor* monitor = PowerMonitor::Get();
+  if (!monitor)
+    return;
+
+  PowerMonitorSource* source = monitor->Source();
+
+  // Suppress duplicate notifications.  Some platforms may
+  // send multiple notifications of the same event.
+  switch (event_id) {
+    case POWER_STATE_EVENT:
+      if (source->UpdateOnBatteryPower())
+          monitor->NotifyPowerStateChange(source->IsOnBatteryPower());

[piman, 2013/07/12 21:09:58]

note: maybe it's benign, but since you release the lock in UpdateOnBatteryPower
and grab it again in IsOnBatteryPower you could have a race where
on_battery_power_ changes (on another thread) in the middle. Does it matter?

[bajones, 2013/07/13 00:33:20]

I doubt it does, but for the sake of avoiding any future questions like this
I've refactored it to handle the locking better (though the code is a bit uglier
for it.)

+      break;
+    case RESUME_EVENT:
+      if (source->suspended_) {
+        source->suspended_ = false;
+        monitor->NotifyResume();
+      }
+      break;
+    case SUSPEND_EVENT:
+      if (!source->suspended_) {
+        source->suspended_ = true;
+        monitor->NotifySuspend();
+      }
+      break;
+  }
+}
+
+}  // namespace base