Fix serialization of content property to always quote

Source/core/css/StylePropertySerializer.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Research In Motion Limited. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. 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 202 matching lines @@
         case CSSPropertyBackgroundColor:
         case CSSPropertyBackgroundImage:
         case CSSPropertyBackgroundOrigin:
         case CSSPropertyBackgroundPositionX:
         case CSSPropertyBackgroundPositionY:
         case CSSPropertyBackgroundSize:
         case CSSPropertyBackgroundRepeatX:
         case CSSPropertyBackgroundRepeatY:
             shorthandPropertyAppeared.set(CSSPropertyBackground - firstCSSProperty);
             continue;
-        case CSSPropertyContent:
-            if (property.value()->isValueList())
-                value = toCSSValueList(property.value())->customCSSText(AlwaysQuoteCSSString);
-            break;
         case CSSPropertyBorderTopWidth:
         case CSSPropertyBorderRightWidth:
         case CSSPropertyBorderBottomWidth:
         case CSSPropertyBorderLeftWidth:
             if (!borderFallbackShorthandProperty)
                 borderFallbackShorthandProperty = CSSPropertyBorderWidth;
         case CSSPropertyBorderTopStyle:
         case CSSPropertyBorderRightStyle:
         case CSSPropertyBorderBottomStyle:
         case CSSPropertyBorderLeftStyle:
@@ skipping 770 matching lines @@
             isInitialValue = false;
         if (!value->isInheritedValue())
             isInheritedValue = false;
         if (isImportant != m_propertySet.propertyIsImportant(shorthand.properties()[i]))
             return false;
     }
     return isInitialValue || isInheritedValue;
 }
 
 }