Make it obvious an HTMLOptionsCollection can only contain HTMLOptionElements

Source/core/html/HTMLSelectElement.h

 /*
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google 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
@@ skipping 79 matching lines @@
     void accessKeySetSelectedIndex(int);
 
     void setMultiple(bool);
 
     void setSize(int);
 
     void setOption(unsigned index, HTMLOptionElement*, ExceptionState&);
     void setLength(unsigned, ExceptionState&);
 
     Element* namedItem(const AtomicString& name);
-    Element* item(unsigned index);
+    HTMLOptionElement* item(unsigned index);
 
     void scrollToSelection();
     void scrollTo(int listIndex);
 
     void listBoxSelectItem(int listIndex, bool allowMultiplySelections, bool shift, bool fireOnChangeNow = true);
 
     bool canSelectAll() const;
     void selectAll();
     int listToOptionIndex(int listIndex) const;
     void listBoxOnChange();
@@ skipping 114 matching lines @@
     bool m_isProcessingUserDrivenChange;
     bool m_multiple;
     bool m_activeSelectionState;
     mutable bool m_shouldRecalcListItems;
     int m_suggestedIndex;
 };
 
 } // namespace
 
 #endif