Update DOMTokenList::value() to return a const reference

Source/core/html/HTMLLinkElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Rob Buis (rwlbuis@gmail.com)
  * Copyright (C) 2011 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 316 matching lines @@
 const AtomicString& HTMLLinkElement::type() const
 {
     return getAttribute(typeAttr);
 }
 
 IconType HTMLLinkElement::iconType() const
 {
     return m_relAttribute.iconType();
 }
 
-String HTMLLinkElement::iconSizes() const
+const AtomicString& HTMLLinkElement::iconSizes() const
 {
     return m_sizes->toString();
 }
 
 DOMSettableTokenList* HTMLLinkElement::sizes() const
 {
     return m_sizes.get();
 }
 
 PassOwnPtr<LinkStyle> LinkStyle::create(HTMLLinkElement* owner)
@@ skipping 259 matching lines @@
 void LinkStyle::ownerRemoved()
 {
     if (m_sheet)
         clearSheet();
 
     if (styleSheetIsLoading())
         removePendingSheet(RemovePendingSheetNotifyLater);
 }
 
 } // namespace WebCore