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

Source/core/frame/DeviceEventControllerBase.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 DeviceEventControllerBase_h
-#define DeviceEventControllerBase_h
-
-#include "core/page/PageLifecycleObserver.h"
-#include "platform/Timer.h"
-#include "platform/heap/Handle.h"
-
-namespace blink {
-
-// Base controller class for registering controllers with a dispatcher.
-// It watches page visibility and calls stopUpdating when page is not visible.
-// It provides a didUpdateData() callback method which is called when new data
-// it available.
-class DeviceEventControllerBase : public PageLifecycleObserver {
-public:
-    void startUpdating();
-    void stopUpdating();
-
-    // This is called when new data becomes available.
-    virtual void didUpdateData() = 0;
-
-protected:
-    explicit DeviceEventControllerBase(Page*);
-    virtual ~DeviceEventControllerBase();
-
-    virtual void registerWithDispatcher() = 0;
-    virtual void unregisterWithDispatcher() = 0;
-
-    // When true initiates a one-shot didUpdateData() when startUpdating() is called.
-    virtual bool hasLastData() = 0;
-
-    bool m_hasEventListener;
-
-private:
-    // Inherited from PageLifecycleObserver.
-    virtual void pageVisibilityChanged() OVERRIDE;
-
-    void oneShotCallback(Timer<DeviceEventControllerBase>*);
-
-    bool m_isActive;
-    Timer<DeviceEventControllerBase> m_timer;
-};
-
-} // namespace blink
-
-#endif // DeviceEventControllerBase_h