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

public/platform/WebDeviceLightListener.h

 // 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.
 
 #ifndef WebDeviceLightListener_h
 #define WebDeviceLightListener_h
 
+#include "WebPlatformEventListener.h"
+
 namespace blink {
 
-class WebDeviceLightListener {
+class WebDeviceLightListener : public WebPlatformEventListener {
 public:
     // This method is called every time new device light data is available.
     virtual void didChangeDeviceLight(double) = 0;
 
     virtual ~WebDeviceLightListener() { }
 };
 
 } // namespace blink
 
 #endif // WebDeviceLightListener_h