[CSS Grid Layout] infinity should be defined as a negative value

Source/core/css/CSSParser-in.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 4701 matching lines @@
     if (currentValue->unit == CSSPrimitiveValue::CSS_FR) {
         double flexValue = currentValue->fValue;
 
         // Fractional unit is a non-negative dimension.
         if (flexValue <= 0)
             return 0;
 
         return cssValuePool().createValue(flexValue, CSSPrimitiveValue::CSS_FR);
     }
 
-    if (!validUnit(currentValue, FLength | FPercent))
+    if (!validUnit(currentValue, FNonNeg | FLength | FPercent))
         return 0;
 
     return createPrimitiveNumericValue(currentValue);
 }
 
 PassRefPtr<CSSValue> CSSParser::parseCounterContent(CSSParserValueList* args, bool counters)
 {
     unsigned numArgs = args->size();
     if (counters && numArgs != 3 && numArgs != 5)
         return 0;
@@ skipping 7007 matching lines @@
 {
     // The tokenizer checks for the construct of an+b.
     // However, since the {ident} rule precedes the {nth} rule, some of those
     // tokens are identified as string literal. Furthermore we need to accept
     // "odd" and "even" which does not match to an+b.
     return equalIgnoringCase(token, "odd") || equalIgnoringCase(token, "even")
         || equalIgnoringCase(token, "n") || equalIgnoringCase(token, "-n");
 }
 
 }