Actually hook server creation into the pub test schedule.

utils/tests/pub/test_pub.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.
 
 /**
  * Test infrastructure for testing pub. Unlike typical unit tests, most pub
  * tests are integration tests that stage some stuff on the file system, run
  * pub, and then validate the results. This library provides an API to build
  * tests like that.
  */
@@ skipping 51 matching lines @@
  *
  * Subsequent calls to [serve] will replace the previous server.
  */
 void serve(String host, int port, [List<Descriptor> contents]) {
   var baseDir = dir("serve-dir", contents);
   if (host == 'localhost') {
     host = '127.0.0.1';
   }
 
   _schedule((_) {
-    _closeServer().transform((_) {
+    return _closeServer().transform((_) {
       _server = new HttpServer();
       _server.defaultRequestHandler = (request, response) {
         var path = request.uri.replaceFirst("/", "").split("/");
         response.persistentConnection = false;
         var stream;
         try {
           stream = baseDir.load(path);
         } catch (var e) {
           response.statusCode = 404;
           response.contentLength = 0;
@@ skipping 728 matching lines @@
 }
 
 /**
  * Schedules a callback to be called after Pub is run with [runPub], even if it
  * fails.
  */
 void _scheduleCleanup(_ScheduledEvent event) {
   if (_scheduledCleanup == null) _scheduledCleanup = [];
   _scheduledCleanup.add(event);
 }