Clean up forward declarations in Source/core/accessibility

Source/core/accessibility/AXListBoxOption.h

 /*
  * Copyright (C) 2008 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 17 matching lines @@
 
 #ifndef AXListBoxOption_h
 #define AXListBoxOption_h
 
 #include "core/accessibility/AXRenderObject.h"
 #include "core/html/HTMLElement.h"
 #include "wtf/Forward.h"
 
 namespace blink {
 
-class AXListBox;
-class Element;
-class HTMLElement;
 class HTMLSelectElement;
 
 class AXListBoxOption final : public AXRenderObject {
 
 private:
     AXListBoxOption(RenderObject*);
 public:
     static PassRefPtr<AXListBoxOption> create(RenderObject*);
     virtual ~AXListBoxOption();
 
@@ skipping 14 matching lines @@
     HTMLSelectElement* listBoxOptionParentNode() const;
     int listBoxOptionIndex() const;
     AXObject* listBoxOptionAXObject(HTMLElement*) const;
 };
 
 DEFINE_AX_OBJECT_TYPE_CASTS(AXListBoxOption, isListBoxOption());
 
 } // namespace blink
 
 #endif // AXListBoxOption_h