Move isValid/isCurrentColor from Color to StyleColor

Source/core/rendering/style/StyleImage.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008 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
  * version 2 of the License, or (at your option) any later version.
@@ skipping 55 matching lines @@
     virtual WrappedImagePtr data() const = 0;
     virtual float imageScaleFactor() const { return 1; }
     virtual bool knownToBeOpaque(const RenderObject*) const = 0;
     virtual CachedImage* cachedImage() const { return 0; }
 
     ALWAYS_INLINE bool isCachedImage() const { return m_isCachedImage; }
     ALWAYS_INLINE bool isPendingImage() const { return m_isPendingImage; }
     ALWAYS_INLINE bool isGeneratedImage() const { return m_isGeneratedImage; }
     ALWAYS_INLINE bool isCachedImageSet() const { return m_isCachedImageSet; }
     
-    static  bool imagesEquivalent(StyleImage* image1, StyleImage* image2)
+    static bool imagesEquivalent(const StyleImage* image1, const StyleImage* image2)
     {
         if (image1 != image2) {
             if (!image1 || !image2)
                 return false;
             return *image1 == *image2;
         }
         return true;
     }
 
 protected:
     StyleImage()
         : m_isCachedImage(false)
         , m_isPendingImage(false)
         , m_isGeneratedImage(false)
         , m_isCachedImageSet(false)
     {
     }
     bool m_isCachedImage:1;
     bool m_isPendingImage:1;
     bool m_isGeneratedImage:1;
     bool m_isCachedImageSet:1;
 };
 
 }
 #endif