[es6] Add appropriate ToString call to String.prototype.normalize

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 1984 matching lines @@
  * If the form is not one of "NFC", "NFD", "NFKC", or "NFKD", then throw
  * a RangeError Exception.
  */
 
 OverrideFunction(GlobalString.prototype, 'normalize', function() {
     if (%_IsConstructCall()) {
       throw MakeTypeError(kOrdinaryFunctionCalledAsConstructor);
     }
 
     CHECK_OBJECT_COERCIBLE(this, "String.prototype.normalize");
+    var s = TO_STRING_INLINE(this);
 
     var formArg = %_Arguments(0);
     var form = IS_UNDEFINED(formArg) ? 'NFC' : TO_STRING_INLINE(formArg);
 
     var NORMALIZATION_FORMS = ['NFC', 'NFD', 'NFKC', 'NFKD'];
 
     var normalizationForm =
         %_CallFunction(NORMALIZATION_FORMS, form, ArrayIndexOf);
     if (normalizationForm === -1) {
       throw MakeRangeError(kNormalizationForm,
           %_CallFunction(NORMALIZATION_FORMS, ', ', ArrayJoin));
     }
 
-    return %StringNormalize(this, normalizationForm);
+    return %StringNormalize(s, normalizationForm);
   }
 );
 
 
 /**
  * Formats a Number object (this) using locale and options values.
  * If locale or options are omitted, defaults are used.
  */
 OverrideFunction(GlobalNumber.prototype, 'toLocaleString', function() {
     if (%_IsConstructCall()) {
@@ skipping 78 matching lines @@
     }
 
     var locales = %_Arguments(0);
     var options = %_Arguments(1);
     return toLocaleDateTime(
         this, locales, options, 'time', 'time', 'dateformattime');
   }
 );
 
 })