Virtualize EventDispatchMediator creation and cleanup calling.

Source/core/events/Event.h

 /*
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2001 Tobias Anton (anton@stud.fbi.fh-darmstadt.de)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 172 matching lines @@
 
     bool isBeingDispatched() const { return eventPhase(); }
 
     double uiCreateTime() const { return m_uiCreateTime; }
     void setUICreateTime(double uiCreateTime) { m_uiCreateTime = uiCreateTime; }
 
     // Events that must not leak across isolated world, similar to how
     // ErrorEvent behaves, can override this method.
     virtual bool canBeDispatchedInWorld(const DOMWrapperWorld&) const { return true; }
 
+    virtual PassRefPtrWillBeRawPtr<EventDispatchMediator> createMediator();
+
     DECLARE_VIRTUAL_TRACE();
 
 protected:
     Event();
     Event(const AtomicString& type, bool canBubble, bool cancelable);
     Event(const AtomicString& type, const EventInit&);
 
     virtual void receivedTarget();
     bool dispatched() const { return m_target; }
 
@@ skipping 18 matching lines @@
     OwnPtrWillBeMember<EventPath> m_eventPath;
     double m_uiCreateTime; // For input events, the time the event was recorded by the UI.
 };
 
 #define DEFINE_EVENT_TYPE_CASTS(typeName) \
     DEFINE_TYPE_CASTS(typeName, Event, event, event->is##typeName(), event.is##typeName())
 
 } // namespace blink
 
 #endif // Event_h