Make deferred loading of message libraries optional

pkg/intl/test/message_extraction/sample_with_messages.dart

 // Copyright (c) 2013, 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 is a program with various [Intl.message] messages. It just prints
  * all of them, and is used for testing of message extraction, translation,
  * and code generation.
  */
 library sample;
@@ skipping 209 matching lines @@
 
 main() {
   var fr = new Intl("fr");
   var english = new Intl("en_US");
   var de = new Intl("de_DE");
   // Throw in an initialize of a null locale to make sure it doesn't throw.
   initializeMessages(null);
 
   // Verify that a translated message isn't initially present.
   var messageInGerman = Intl.withLocale('de_DE', message1);
-  test("Locales don't work before they're initialized", ()
-      => expect(messageInGerman, "This is a message"));
+  expect(messageInGerman, "This is a message");
 
   var f1 = initializeMessages(fr.locale)
       // Since English has the one message which is always translated, we
       // can't print it until French is ready.
       .then((_) => printStuff(english))
       .then((_) => printStuff(fr));
   var f2 = initializeMessages('de-de').then((_) => printStuff(de));
   return Future.wait([f1, f2]);
 }