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

Source/modules/gamepad/GamepadDispatcher.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/gamepad/GamepadDispatcher.h"
 
 #include "modules/gamepad/NavigatorGamepad.h"
 #include "public/platform/Platform.h"
 #include "wtf/TemporaryChange.h"
@@ skipping 34 matching lines @@
     ASSERT(index < blink::WebGamepads::itemsLengthCap);
     ASSERT(connected == gamepad.connected);
 
     m_latestChange.pad = gamepad;
     m_latestChange.index = index;
     notifyControllers();
 }
 
 void GamepadDispatcher::startListening()
 {
-    blink::Platform::current()->setGamepadListener(this);
+    blink::Platform::current()->startListening(WebPlatformEventGamepad, this);
 }
 
 void GamepadDispatcher::stopListening()
 {
-    blink::Platform::current()->setGamepadListener(0);
+    blink::Platform::current()->stopListening(WebPlatformEventGamepad);
 }
 
 } // namespace blink