Remove the Element.prefix setter

Source/core/dom/Element.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2013 Apple 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
  * License as published by the Free Software Foundation; either
@@ skipping 480 matching lines @@
     IntSize savedLayerScrollOffset() const;
     void setSavedLayerScrollOffset(const IntSize&);
 
     ActiveAnimations* activeAnimations() const;
     ActiveAnimations& ensureActiveAnimations();
     bool hasActiveAnimations() const;
 
     InputMethodContext& inputMethodContext();
     bool hasInputMethodContext() const;
 
-    void setPrefix(const AtomicString&, ExceptionState&);
-
     void synchronizeAttribute(const AtomicString& localName) const;
 
     MutableStylePropertySet& ensureMutableInlineStyle();
     void clearMutableInlineStyleIfEmpty();
 
     void setTabIndex(int);
     virtual short tabIndex() const OVERRIDE;
 
     virtual void trace(Visitor*) OVERRIDE;
 
@@ skipping 365 matching lines @@
     template <> inline bool isElementOfType<const thisType>(const Element& element) { return element.predicate; } \
     DEFINE_NODE_TYPE_CASTS(thisType, predicate)
 
 #define DEFINE_ELEMENT_TYPE_CASTS_WITH_FUNCTION(thisType) \
     template <> inline bool isElementOfType<const thisType>(const Element& element) { return is##thisType(element); } \
     DEFINE_NODE_TYPE_CASTS_WITH_FUNCTION(thisType)
 
 } // namespace
 
 #endif