Allow ICU to normalize time zones

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 1556 matching lines @@
     timeZone: {writable: true},
     timeZoneName: {writable: true},
     tz: {value: tz, writable: true},
     weekday: {writable: true},
     year: {writable: true}
   });
 
   var formatter = %CreateDateTimeFormat(
     requestedLocale, {skeleton: ldmlString, timeZone: tz}, resolved);
 
-  if (!IS_UNDEFINED(tz) && tz !== resolved.timeZone) {
+  if (resolved.timeZone === "Etc/Unknown") {
     throw MakeRangeError(kUnsupportedTimeZone, tz);
   }
 
   %MarkAsInitializedIntlObjectOfType(dateFormat, 'dateformat', formatter);
   ObjectDefineProperty(dateFormat, 'resolved', {value: resolved});
 
   return dateFormat;
 }
 
 
@@ skipping 525 matching lines @@
     }
 
     var locales = %_Arguments(0);
     var options = %_Arguments(1);
     return toLocaleDateTime(
         this, locales, options, 'time', 'time', 'dateformattime');
   }
 );
 
 })