Don't pretend that text-decoration is a shorthand in computed style.

Source/core/css/CSSComputedStyleDeclaration.cpp

 /*
  * Copyright (C) 2004 Zack Rusin <zack@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2011 Sencha, Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
@@ skipping 2180 matching lines @@
             return cssValuePool().createValue(style->rubyPosition());
         case CSSPropertyScrollBehavior:
             return cssValuePool().createValue(style->scrollBehavior());
         case CSSPropertyTableLayout:
             return cssValuePool().createValue(style->tableLayout());
         case CSSPropertyTextAlign:
             return cssValuePool().createValue(style->textAlign());
         case CSSPropertyTextAlignLast:
             return cssValuePool().createValue(style->textAlignLast());
         case CSSPropertyTextDecoration:
-            return valuesForShorthandProperty(textDecorationShorthand());
+            if (RuntimeEnabledFeatures::css3TextDecorationsEnabled())
+                return valuesForShorthandProperty(textDecorationShorthand());
+            // Fall through.
         case CSSPropertyTextDecorationLine:
             return renderTextDecorationFlagsToCSSValue(style->textDecoration());
         case CSSPropertyTextDecorationStyle:
             return valueForTextDecorationStyle(style->textDecorationStyle());
         case CSSPropertyTextDecorationColor:
             return currentColorOrValidColor(*style, style->textDecorationColor());
         case CSSPropertyTextJustify:
             return cssValuePool().createValue(style->textJustify());
         case CSSPropertyTextUnderlinePosition:
             return cssValuePool().createValue(style->textUnderlinePosition());
@@ skipping 843 matching lines @@
     static const CSSPropertyID propertiesAfterSlashSeperator[3] = { CSSPropertyBackgroundSize, CSSPropertyBackgroundOrigin,
                                                                     CSSPropertyBackgroundClip };
 
     RefPtrWillBeRawPtr<CSSValueList> list = CSSValueList::createSlashSeparated();
     list->append(valuesForShorthandProperty(StylePropertyShorthand(CSSPropertyBackground, propertiesBeforeSlashSeperator, WTF_ARRAY_LENGTH(propertiesBeforeSlashSeperator))));
     list->append(valuesForShorthandProperty(StylePropertyShorthand(CSSPropertyBackground, propertiesAfterSlashSeperator, WTF_ARRAY_LENGTH(propertiesAfterSlashSeperator))));
     return list.release();
 }
 
 } // namespace WebCore