Add support for "image-set"

third_party/WebKit/Source/core/css/CSSImageSetValue.cpp

 /*
  * Copyright (C) 2012 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 113 matching lines @@
             m_cachedImage = StyleInvalidImage::create(image.imageURL);
         m_cachedScaleFactor = deviceScaleFactor;
     }
 
     return m_cachedImage.get();
 }
 
 String CSSImageSetValue::customCSSText() const
 {
     StringBuilder result;
-    result.append("-webkit-image-set(");
+    result.append("image-set(");
 
     size_t length = this->length();
     size_t i = 0;
     while (i < length) {
         if (i > 0)
             result.append(", ");
 
         const CSSValue& imageValue = item(i);
         result.append(imageValue.cssText());
         result.append(' ');
@@ skipping 31 matching lines @@
 CSSImageSetValue* CSSImageSetValue::valueWithURLsMadeAbsolute()
 {
     CSSImageSetValue* value = CSSImageSetValue::create();
     for (auto& item : *this)
         item->isImageValue() ? value->append(*toCSSImageValue(*item).valueWithURLMadeAbsolute()) : value->append(*item);
     return value;
 }
 
 
 } // namespace blink