[es6] Fix String.prototype.normalize to properly validate argument

src/i18n.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // ECMAScript 402 API implementation.
 
 /**
  * Intl object is a single object that has some named properties,
  * all of which are constructors.
  */
@@ skipping 1971 matching lines @@
 );
 
 
 /**
  * Unicode normalization. This method is called with one argument that
  * specifies the normalization form.
  * If none is specified, "NFC" is assumed.
  * If the form is not one of "NFC", "NFD", "NFKC", or "NFKD", then throw
  * a RangeError Exception.
  */
-OverrideFunction(GlobalString.prototype, 'normalize', function(that) {
+OverrideFunction(GlobalString.prototype, 'normalize', function(form) {
     if (%_IsConstructCall()) {
       throw MakeTypeError(kOrdinaryFunctionCalledAsConstructor);
     }
 
     CHECK_OBJECT_COERCIBLE(this, "String.prototype.normalize");
 
-    var form = GlobalString(%_Arguments(0) || 'NFC');
+    form = IS_UNDEFINED(form) ? 'NFC' : form;
 
     var NORMALIZATION_FORMS = ['NFC', 'NFD', 'NFKC', 'NFKD'];
 
     var normalizationForm =
         %_CallFunction(NORMALIZATION_FORMS, form, ArrayIndexOf);
     if (normalizationForm === -1) {
       throw MakeRangeError(kNormalizationForm,
           %_CallFunction(NORMALIZATION_FORMS, ', ', ArrayJoin));
     }
 
@@ skipping 89 matching lines @@
     }
 
     var locales = %_Arguments(0);
     var options = %_Arguments(1);
     return toLocaleDateTime(
         this, locales, options, 'time', 'time', 'dateformattime');
   }
 );
 
 })