Clean up forward declarations in Source/core/accessibility

Source/core/accessibility/AXMenuListOption.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 AXMenuListOption_h
 #define AXMenuListOption_h
 
 #include "core/accessibility/AXMockObject.h"
 
 namespace blink {
 
-class AXMenuListPopup;
 class HTMLElement;
 
 class AXMenuListOption final : public AXMockObject {
 public:
     static PassRefPtr<AXMenuListOption> create() { return adoptRef(new AXMenuListOption); }
 
     void setElement(HTMLElement*);
 
 private:
     AXMenuListOption();
@@ skipping 15 matching lines @@
     virtual bool computeAccessibilityIsIgnored() const override;
 
     RefPtrWillBePersistent<HTMLElement> m_element;
 };
 
 DEFINE_AX_OBJECT_TYPE_CASTS(AXMenuListOption, isMenuListOption());
 
 } // namespace blink
 
 #endif // AXMenuListOption_h