Add async initialization for Intl.message and an example

pkg/intl/lib/lazy_locale_data.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * This defines a class for loading locale data incrementally from
  * an external source as JSON. The external sources expected are either
  * local files or via HTTP request.
  */
 
@@ skipping 90 matching lines @@
       'Locale $localeName has no data available');}
 
   /**
    * Initialize for locale. Internal use only. As a user, call
    * initializeDateFormatting instead.
    */
   Future initLocale(String localeName) {
     var data = _reader.read(localeName);
     return jsonData(data).transform( (input) {
         map[localeName] = _creationFunction(input);});
-    return data;
   }
 
   /**
    * Given a Future [input] whose value is expected to be a string in JSON form,
    * return another future that parses the JSON into a usable format.
    */
   Future jsonData(Future input) {
     return input.transform( (response) => JSON.parse(response));
   }
 }