Add CSS parser recovery from errors while parsing @-webkit-keyframes key values.

Source/core/css/CSSGrammar.y.in

 /*
  *  Copyright (C) 2002-2003 Lars Knoll (knoll@kde.org)
  *  Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  *  Copyright (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *  Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  *  Copyright (C) 2012 Intel Corporation. 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 837 matching lines @@
 
 key:
     maybe_unary_operator PERCENTAGE { $$.id = 0; $$.isInt = false; $$.fValue = $1 * $2; $$.unit = CSSPrimitiveValue::CSS_NUMBER; }
     | IDENT {
         $$.id = 0; $$.isInt = false; $$.unit = CSSPrimitiveValue::CSS_NUMBER;
         CSSParserString& str = $1;
         if (str.equalIgnoringCase("from"))
             $$.fValue = 0;
         else if (str.equalIgnoringCase("to"))
             $$.fValue = 100;
-        else
+        else {
+            $$.unit = 0;
             YYERROR;
+        }
+    }
+    | error {
+        $$.unit = 0;
     }
     ;
 
 before_page_rule:
     /* empty */ {
         parser->startRuleHeader(CSSRuleSourceData::PAGE_RULE);
     }
     ;
 
 page:
@@ skipping 1131 matching lines @@
     }
     ;
 
 error_location: {
         $$ = parser->currentLocation();
     }
     ;
 
 %%