[i18n] Ensure [[ToString]] conversion of time zone names.

src/js/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 1767 matching lines @@
 /**
  * Returns canonical Area/Location(/Location) name, or throws an exception
  * if the zone name is invalid IANA name.
  */
 function canonicalizeTimeZoneID(tzID) {
   // Skip undefined zones.
   if (IS_UNDEFINED(tzID)) {
     return tzID;
   }
 
+  // Convert zone name to string.
+  tzID = TO_STRING(tzID);
+
   // Special case handling (UTC, GMT).
   var upperID = %StringToUpperCase(tzID);
   if (upperID === 'UTC' || upperID === 'GMT' ||
       upperID === 'ETC/UTC' || upperID === 'ETC/GMT') {
     return 'UTC';
   }
 
   // TODO(jshin): Add support for Etc/GMT[+-]([1-9]|1[0-2])
 
   // We expect only _, '-' and / beside ASCII letters.
@@ skipping 451 matching lines @@
   }
 );
 
 utils.Export(function(to) {
   to.AddBoundMethod = AddBoundMethod;
   to.IntlParseDate = IntlParseDate;
   to.IntlParseNumber = IntlParseNumber;
 });
 
 })