Make Completers asynchronous.

tests/standalone/io/http_server_early_client_close_test.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.
 
 import "package:expect/expect.dart";
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 void sendData(List<int> data, int port) {
@@ skipping 107 matching lines @@
     makeRequest() {
       Socket.connect("127.0.0.1", server.port).then((socket) {
         var data = "GET / HTTP/1.1\r\nContent-Length: 0\r\n\r\n";
         socket.write(data);
         socket.close();
         socket.done.then((_) {
           socket.destroy();
           if (++count < 10) {
             makeRequest();
           } else {
-            server.close();
+            runAsync(server.close);
           }
         });
       });
     }
     makeRequest();
   });
 }
 
 void testEarlyClose3() {
   HttpServer.bind("127.0.0.1", 0).then((server) {
@@ skipping 18 matching lines @@
           socket.done.catchError((_) {});
         });
   });
 }
 
 void main() {
   testEarlyClose1();
   testEarlyClose2();
   testEarlyClose3();
 }