Clean up forward declarations in Source/core/accessibility

Source/core/accessibility/AXMenuList.h

 /*
  * Copyright (C) 2010 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 12 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef AXMenuList_h
 #define AXMenuList_h
 
 #include "core/accessibility/AXRenderObject.h"
 
 namespace blink {
 
-class AXMenuList;
-class AXMenuListPopup;
-class HTMLOptionElement;
 class RenderMenuList;
 
 class AXMenuList final : public AXRenderObject {
 public:
     static PassRefPtr<AXMenuList> create(RenderMenuList* renderer);
 
     virtual bool isCollapsed() const override;
     virtual bool press() const override;
 
     void didUpdateActiveOption(int optionIndex);
 
 private:
     explicit AXMenuList(RenderMenuList*);
 
     virtual bool isMenuList() const override { return true; }
     virtual AccessibilityRole roleValue() const override { return PopUpButtonRole; }
     virtual bool canSetFocusAttribute() const override;
 
     virtual void addChildren() override;
     virtual void childrenChanged() override;
 };
 
 DEFINE_AX_OBJECT_TYPE_CASTS(AXMenuList, isMenuList());
 
 } // namespace blink
 
 #endif // AXMenuList_h