Adding support for color interpolation hints to CSS gradients.

Source/core/css/CSSGradientValue.h

 /*
  * Copyright (C) 2008 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 47 matching lines @@
     CSSGradientColorStop() : m_colorIsDerivedFromElement(false) { };
     RefPtrWillBeMember<CSSPrimitiveValue> m_position; // percentage or length
     RefPtrWillBeMember<CSSPrimitiveValue> m_color;
     Color m_resolvedColor;
     bool m_colorIsDerivedFromElement;
     bool operator==(const CSSGradientColorStop& other) const
     {
         return compareCSSValuePtr(m_color, other.m_color)
             && compareCSSValuePtr(m_position, other.m_position);
     }
+    bool isHint() const
+    {
+        ASSERT(m_color || m_position);
+        return !m_color;
+    }
 
     void trace(Visitor*);
 };
 
 } // namespace blink
 
 
 // We have to declare the VectorTraits specialization before CSSGradientValue
 // declares its inline capacity vector below.
 WTF_ALLOW_MOVE_AND_INIT_WITH_MEM_FUNCTIONS(blink::CSSGradientColorStop);
@@ skipping 177 matching lines @@
 
     RefPtrWillBeMember<CSSPrimitiveValue> m_endHorizontalSize;
     RefPtrWillBeMember<CSSPrimitiveValue> m_endVerticalSize;
 };
 
 DEFINE_CSS_VALUE_TYPE_CASTS(CSSRadialGradientValue, isRadialGradientValue());
 
 } // namespace blink
 
 #endif // CSSGradientValue_h