Stylesheet rule.cssText of content property should be quoted when the value is string.

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 68 matching lines @@
             continue;
         case CSSPropertyBackgroundPositionY:
             positionYPropertyIndex = n;
             continue;
         case CSSPropertyBackgroundRepeatX:
             repeatXPropertyIndex = n;
             continue;
         case CSSPropertyBackgroundRepeatY:
             repeatYPropertyIndex = n;
             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 109 matching lines @@
         unsigned shortPropertyIndex = shorthandPropertyID - firstCSSProperty;
         if (shorthandPropertyID) {
             if (shorthandPropertyUsed.get(shortPropertyIndex))
                 continue;
             if (!shorthandPropertyAppeared.get(shortPropertyIndex) && value.isNull())
                 value = m_propertySet.getPropertyValue(shorthandPropertyID);
             shorthandPropertyAppeared.set(shortPropertyIndex);
         }
 
         if (!value.isNull()) {
-            propertyID = shorthandPropertyID;
-            shorthandPropertyUsed.set(shortPropertyIndex);
+            if (shorthandPropertyID) {
+                propertyID = shorthandPropertyID;
+                shorthandPropertyUsed.set(shortPropertyIndex);
+            }
         } else
             value = property.value()->cssText();
 
         if (value == "initial" && !CSSProperty::isInheritedProperty(propertyID))
             continue;
 
         if (numDecls++)
             result.append(' ');
         result.append(getPropertyName(propertyID));
         result.appendLiteral(": ");
@@ skipping 517 matching lines @@
         if (!result.isEmpty())
             result.append(' ');
         result.append(value);
     }
     if (isInitialOrInherit(commonValue))
         return commonValue;
     return result.isEmpty() ? String() : result.toString();
 }
 
 }