Avoid reparsing keyframe selectors

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 829 matching lines @@
         $$->addValue(parser->sinkFloatingValue($1));
     }
     | key_list maybe_space ',' maybe_space key {
         $$ = $1;
         if ($$)
             $$->addValue(parser->sinkFloatingValue($5));
     }
     ;
 
 key:
-    maybe_unary_operator PERCENTAGE { $$.id = 0; $$.isInt = false; $$.fValue = $1 * $2; $$.unit = CSSPrimitiveValue::CSS_NUMBER; }
+    maybe_unary_operator PERCENTAGE {
+        $$.id = 0; $$.isInt = false;
+        if ($1 > 0 && $2 <= 100) {
+            $$.fValue = $1 * $2; $$.unit = CSSPrimitiveValue::CSS_NUMBER;
+        } else {
+            $$.fValue = 0; $$.unit = CSSPrimitiveValue::CSS_UNKNOWN;
+        }
+    }
     | 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
             YYERROR;
     }
@@ skipping 1140 matching lines @@
     }
     ;
 
 error_location: {
         $$ = parser->currentLocation();
     }
     ;
 
 %%