Make sure to don't close the HTTP Server until all the headers have been flushed.

tests/standalone/src/io/HttpServerTest.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.
 
 #import("dart:io");
 #import("dart:isolate");
 
 void testListenOn() {
   ServerSocket socket = new ServerSocket("127.0.0.1", 0, 5);
 
   socket.onError = (Exception e) {
     Expect.fail("ServerSocket closed unexpected");
   };
 
   void test(void onDone()) {
     HttpServer server = new HttpServer();
     Expect.throws(() => server.port);
 
     ReceivePort serverPort = new ReceivePort();
     server.onRequest = (HttpRequest request, HttpResponse response) {
       request.inputStream.onClosed = () {
         response.outputStream.close();
-        server.close();
-        Expect.throws(() => server.port);
         serverPort.close();
-        onDone();
       };
     };
 
     server.onError = (Exception e) {
       Expect.fail("Unexpected error in Http Server: $e");
     };
 
     server.listenOn(socket);
     Expect.equals(socket.port, server.port);
 
     HttpClient client = new HttpClient();
     HttpClientConnection conn = client.get("127.0.0.1", socket.port, "/");
     conn.onRequest = (HttpClientRequest request) {
       request.outputStream.close();
     };
     ReceivePort clientPort = new ReceivePort();
     conn.onResponse = (HttpClientResponse response) {
       response.inputStream.onClosed = () {
         client.shutdown();
         clientPort.close();
+        server.close();
+        Expect.throws(() => server.port);
+        onDone();
       };
     };
     conn.onError = (Exception e) {
-      Expect.fail("Unexpected error in Http Client");
+      Expect.fail("Unexpected error in Http Client: $e");
     };
   };
 
   // Test two connection after each other.
   test(() {
     test(() {
       socket.close();
     });
   });
 }
 
 void main() {
   testListenOn();
 }