Clean up after getPropertyCSSValue

Source/core/css/CSSGridLineNamesValue.cpp

 /*
  * Copyright (C) 2013 Igalia, S.L. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 25 matching lines @@
 String CSSGridLineNamesValue::customCSSText() const
 {
     return "(" + CSSValueList::customCSSText() + ")";
 }
 
 CSSGridLineNamesValue::CSSGridLineNamesValue()
     : CSSValueList(GridLineNamesClass, SpaceSeparator)
 {
 }
 
-PassRefPtrWillBeRawPtr<CSSGridLineNamesValue> CSSGridLineNamesValue::cloneForCSSOM() const
-{
-    return adoptRefWillBeNoop(new CSSGridLineNamesValue(*this));
-}
-
 }