CSSValue Immediates: Change CSSValue to an object instead of a pointer

Source/core/css/CSSBorderImage.h

 /*
  * Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies)
  *
  * 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
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #ifndef CSSBorderImage_h
 #define CSSBorderImage_h
 
 #include "core/css/CSSBorderImageSliceValue.h"
 #include "core/css/CSSValueList.h"
 #include "wtf/PassRefPtr.h"
 
 namespace blink {
 
-PassRefPtrWillBeRawPtr<CSSValueList> createBorderImageValue(PassRefPtrWillBeRawPtr<CSSValue> image, PassRefPtrWillBeRawPtr<CSSValue> imageSlice, PassRefPtrWillBeRawPtr<CSSValue> borderSlice,
-    PassRefPtrWillBeRawPtr<CSSValue> outset, PassRefPtrWillBeRawPtr<CSSValue> repeat);
+PassRefPtrWillBeRawPtr<CSSValueList> createBorderImageValue(NullableCSSValue image, NullableCSSValue imageSlice, NullableCSSValue borderSlice,
+    NullableCSSValue outset, NullableCSSValue repeat);
 
 } // namespace blink
 
 #endif // CSSBorderImage_h