Fix idle connection pool issue in dart:io's HttpClient

dart/tests/standalone/io/http_cross_process_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';
 
 const int NUM_SERVERS = 10;
@@ skipping 36 matching lines @@
       print(result.stderr);
       Expect.fail('Client subprocess exit code: ${result.exitCode}');
     }
   });
 }
 
 runClient(int port) {
   var client = new HttpClient();
   client.get('127.0.0.1', port, "/")
       .then((request) => request.close())
-      .then((response) => response.listen((data) {},
-                                          onDone: () => print('SUCCESS')));
+      .then((response) => response.drain())
+      .then((_) => client.close())
+      .then((_) => print('SUCCESS'));
 }