Make Event RefCountedGarbageCollected and implement trace() methods to the Event hierarcy

Source/core/events/MouseEvent.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, 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 84 matching lines @@
     MouseEvent(const AtomicString& type, bool canBubble, bool cancelable, PassRefPtr<AbstractView>,
         int detail, int screenX, int screenY, int pageX, int pageY,
         int movementX, int movementY,
         bool ctrlKey, bool altKey, bool shiftKey, bool metaKey, unsigned short button,
         PassRefPtr<EventTarget> relatedTarget, PassRefPtrWillBeRawPtr<Clipboard>, bool isSimulated);
 
     MouseEvent(const AtomicString& type, const MouseEventInit&);
 
     MouseEvent();
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     unsigned short m_button;
     bool m_buttonDown;
     RefPtr<EventTarget> m_relatedTarget;
-    RefPtrWillBePersistent<Clipboard> m_clipboard;
+    RefPtrWillBeMember<Clipboard> m_clipboard;
 };
 
 class SimulatedMouseEvent FINAL : public MouseEvent {
 public:
     static PassRefPtr<SimulatedMouseEvent> create(const AtomicString& eventType, PassRefPtr<AbstractView>, PassRefPtr<Event> underlyingEvent);
     virtual ~SimulatedMouseEvent();
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     SimulatedMouseEvent(const AtomicString& eventType, PassRefPtr<AbstractView>, PassRefPtr<Event> underlyingEvent);
 };
 
 class MouseEventDispatchMediator FINAL : public EventDispatchMediator {
 public:
     enum MouseEventType { SyntheticMouseEvent, NonSyntheticMouseEvent};
     static PassRefPtr<MouseEventDispatchMediator> create(PassRefPtr<MouseEvent>, MouseEventType = NonSyntheticMouseEvent);
 
 private:
     explicit MouseEventDispatchMediator(PassRefPtr<MouseEvent>, MouseEventType);
     MouseEvent* event() const;
 
     virtual bool dispatchEvent(EventDispatcher*) const OVERRIDE;
     bool isSyntheticMouseEvent() const { return m_mouseEventType == SyntheticMouseEvent; }
     MouseEventType m_mouseEventType;
 };
 
 DEFINE_EVENT_TYPE_CASTS(MouseEvent);
 
 } // namespace WebCore
 
 #endif // MouseEvent_h