Implement base::PowerMonitor::IsOnBatteryPower() for OSX.

base/power_monitor/power_monitor_device_source_android.cc

Index: base/power_monitor/power_monitor_device_source_android.cc
diff --git a/base/power_monitor/power_monitor_device_source_android.cc b/base/power_monitor/power_monitor_device_source_android.cc
index c584a0c15b57f7b5e5a2a21a9baa0dce6e8ce3ef..fd5635c1913a663503c461ce9038e440a3ab71e8 100644
--- a/base/power_monitor/power_monitor_device_source_android.cc
+++ b/base/power_monitor/power_monitor_device_source_android.cc
@@ -18,7 +18,9 @@ void ProcessPowerEventHelper(PowerMonitorSource::PowerEvent event) {
 
 namespace android {
 
-// Native implementation of PowerMonitor.java.
+// Native implementation of PowerMonitor.java. Note: This will be invoked by
+// PowerMonitor.java shortly after startup to set the correct initial value for
+// "is on battery power."
 void OnBatteryChargingChanged(JNIEnv* env, const JavaParamRef<jclass>& clazz) {
   ProcessPowerEventHelper(PowerMonitorSource::POWER_STATE_EVENT);
 }