Clean up forward declarations in Source/core/events

Source/core/html/track/TextTrackCue.h

 /*
  * Copyright (C) 2011 Google Inc.  All rights reserved.
  * Copyright (C) 2012, 2013 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 21 matching lines @@
 #ifndef TextTrackCue_h
 #define TextTrackCue_h
 
 #include "core/events/EventTarget.h"
 #include "core/html/HTMLDivElement.h"
 #include "platform/heap/Handle.h"
 #include "wtf/RefCounted.h"
 
 namespace blink {
 
+class TextTrack;
+
 class TextTrackCue : public RefCountedWillBeGarbageCollectedFinalized<TextTrackCue>, public EventTargetWithInlineData {
     DEFINE_WRAPPERTYPEINFO();
     REFCOUNTED_EVENT_TARGET(TextTrackCue);
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(TextTrackCue);
 public:
     static const AtomicString& cueShadowPseudoId()
     {
         DEFINE_STATIC_LOCAL(const AtomicString, cue, ("cue", AtomicString::ConstructFromLiteral));
         return cue;
     }
@@ skipping 59 matching lines @@
 
     RawPtrWillBeMember<TextTrack> m_track;
 
     bool m_isActive : 1;
     bool m_pauseOnExit : 1;
 };
 
 } // namespace blink
 
 #endif // TextTrackCue_h