Add support for RelatedEvent.

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 126 matching lines @@
     bool hasInterface(const AtomicString&) const;
 
     // These events are general classes of events.
     virtual bool isUIEvent() const;
     virtual bool isMouseEvent() const;
     virtual bool isFocusEvent() const;
     virtual bool isKeyboardEvent() const;
     virtual bool isTouchEvent() const;
     virtual bool isGestureEvent() const;
     virtual bool isWheelEvent() const;
+    virtual bool isRelatedEvent() const;
 
     // Drag events are a subset of mouse events.
     virtual bool isDragEvent() const;
 
     // These events lack a DOM interface.
     virtual bool isClipboardEvent() const;
     virtual bool isBeforeTextInsertedEvent() const;
 
     virtual bool isBeforeUnloadEvent() const;
 
@@ skipping 52 matching lines @@
     RefPtrWillBeMember<Event> m_underlyingEvent;
     OwnPtrWillBeMember<EventPath> m_eventPath;
 };
 
 #define DEFINE_EVENT_TYPE_CASTS(typeName) \
     DEFINE_TYPE_CASTS(typeName, Event, event, event->is##typeName(), event.is##typeName())
 
 } // namespace blink
 
 #endif // Event_h