Treat standalone default/initial/inherit in font-family as invalid

Source/core/css/parser/CSSPropertyParser.cpp

 /*
  * Copyright (C) 2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  *
@@ skipping 4618 matching lines @@
 
     while (value) {
         CSSParserValue* nextValue = m_valueList->next();
         bool nextValBreaksFont = !nextValue || isComma(nextValue);
         bool nextValIsFontName = nextValue &&
             ((nextValue->id >= CSSValueSerif && nextValue->id <= CSSValueWebkitBody) ||
             (nextValue->unit == CSSPrimitiveValue::CSS_STRING || nextValue->unit == CSSPrimitiveValue::CSS_IDENT));
 
         if (isCSSWideKeyword(*value) && !inFamily) {
             if (nextValBreaksFont)
-                value = m_valueList->next();
+                return nullptr;
             else if (nextValIsFontName)
                 value = nextValue;
             continue;
         }
 
         if (value->id >= CSSValueSerif && value->id <= CSSValueWebkitBody) {
             if (inFamily)
                 familyBuilder.add(value->string);
             else if (nextValBreaksFont || !nextValIsFontName)
                 list->append(cssValuePool().createIdentifierValue(value->id));
@@ skipping 3840 matching lines @@
         }
     }
 
     if (!list->length())
         return nullptr;
 
     return list.release();
 }
 
 } // namespace blink