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

Source/core/css/CSSGrammar.y.in

Index: Source/core/css/CSSGrammar.y.in
diff --git a/Source/core/css/CSSGrammar.y.in b/Source/core/css/CSSGrammar.y.in
index 9543cbead6f9f1da23567ec934cb740a2cb4b194..08f5d070c4ac42619dc482b5bc00dfcb1a92e491 100644
--- a/Source/core/css/CSSGrammar.y.in
+++ b/Source/core/css/CSSGrammar.y.in
@@ -855,8 +855,13 @@ key:
             $$.fValue = 0;
         else if (str.equalIgnoringCase("to"))
             $$.fValue = 100;
-        else
+        else {
+            $$.unit = CSSParserValue::Invalid;
             YYERROR;
+        }
+    }
+    | error {
+        $$.unit = CSSParserValue::Invalid;
     }
     ;