Introduce PlatformEvent to handle Device events, Battery events and Gamepad events.

Source/modules/battery/BatteryDispatcher.cpp

 // Copyright 2014 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 "config.h"
 #include "modules/battery/BatteryDispatcher.h"
 
 #include "modules/battery/BatteryStatus.h"
 #include "platform/NotImplemented.h"
 #include "public/platform/Platform.h"
@@ skipping 20 matching lines @@
     notifyControllers();
 }
 
 BatteryStatus* BatteryDispatcher::latestData()
 {
     return m_batteryStatus.get();
 }
 
 void BatteryDispatcher::startListening()
 {
-    blink::Platform::current()->setBatteryStatusListener(this);
+    blink::Platform::current()->startListening(WebPlatformEventBattery, this);
 }
 
 void BatteryDispatcher::stopListening()
 {
-    blink::Platform::current()->setBatteryStatusListener(0);
+    blink::Platform::current()->stopListening(WebPlatformEventBattery);
     m_batteryStatus.clear();
 }
 
 }