Make base::PowerMonitor work on Chrome OS.

base/power_monitor/power_monitor_device_source.h

Index: base/power_monitor/power_monitor_device_source.h
diff --git a/base/power_monitor/power_monitor_device_source.h b/base/power_monitor/power_monitor_device_source.h
index 37b065a77c6a16498fc07993a7eb5b1276ad606a..d29ec0a499d81d0dc0a80af69b34a626edaa3563 100644
--- a/base/power_monitor/power_monitor_device_source.h
+++ b/base/power_monitor/power_monitor_device_source.h
@@ -51,6 +51,16 @@ class BASE_EXPORT PowerMonitorDeviceSource : public PowerMonitorSource {
 #endif  // OS_IOS
 #endif  // OS_MACOSX
 
+#if defined(OS_CHROMEOS)
+  // On Chrome OS, Chrome receives power-related events from powerd, the system
+  // power daemon, via D-Bus signals received on the UI thread. base can't
+  // directly depend on that code, so this class instead exposes static methods
+  // so that events can be passed in.
+  static void SetPowerSource(bool on_battery);
+  static void HandleSystemSuspending();
+  static void HandleSystemResumed();
+#endif
+
  private:
 #if defined(OS_WIN)
   // Represents a message-only window for power message handling on Windows.