chromeos: Use EventRouterForwarder to disptch systemPrivate extension events

chrome/browser/extensions/system/system_api.h

Index: chrome/browser/extensions/system/system_api.h
diff --git a/chrome/browser/extensions/system/system_api.h b/chrome/browser/extensions/system/system_api.h
index 5e26978d8aa8107d4d47752836e0c5b29a1b0560..ba100bbb65b1b78caa329e1e3eeff111e3a5dd18 100644
--- a/chrome/browser/extensions/system/system_api.h
+++ b/chrome/browser/extensions/system/system_api.h
@@ -35,9 +35,16 @@ class GetUpdateStatusFunction : public SyncExtensionFunction {
   virtual bool RunImpl() OVERRIDE;
 };
 
+// Dispatches systemPrivate.onBrightnessChanged event for extensions.
 void DispatchBrightnessChangedEvent(int brightness, bool user_initiated);
+
+// Dispatches systemPrivate.onVolumeChanged event for extensions.
 void DispatchVolumeChangedEvent(double volume, bool is_volume_muted);
+
+// Dispatches systemPrivate.onScreenChanged event for extensions.
 void DispatchScreenUnlockedEvent();
+
+// Dispatches systemPrivate.onWokeUp event for extensions.
 void DispatchWokeUpEvent();
 
 }  // namespace extensions