Make sure <url>s are being serialized according to spec

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

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2012 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 879 matching lines @@
         text = formatNumber(m_value.num, unitTypeToString(type()));
         break;
     case UnitType::CustomIdentifier:
         text = quoteCSSStringIfNeeded(m_value.string);
         break;
     case UnitType::String: {
         text = serializeString(m_value.string);
         break;
     }
     case UnitType::URI:
-        text = "url(" + quoteCSSURLIfNeeded(m_value.string) + ")";
+        text = serializeURI(m_value.string);
         break;
     case UnitType::ValueID:
         text = valueName(m_value.valueID);
         break;
     case UnitType::PropertyID:
         text = propertyName(m_value.propertyID);
         break;
     case UnitType::RGBColor: {
         text = Color(m_value.rgbcolor).serializedAsCSSComponentValue();
         break;
@@ skipping 79 matching lines @@
         visitor->trace(m_value.calc);
         break;
     default:
         break;
     }
 #endif
     CSSValue::traceAfterDispatch(visitor);
 }
 
 } // namespace blink