Fix https_bad_certificate_test.

tests/standalone/io/https_bad_certificate_client.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.
 
 // Client for https_bad_certificate_test, that runs in a subprocess.
 // It verifies that the client bad certificate callback works in HttpClient.
 
 import "dart:async";
 import "dart:io";
 
@@ skipping 24 matching lines @@
     if (result == 'false') return false;
     return result;
   }
 
   HttpClient client = new HttpClient();
 
   var testFutures = [];  // The three async getUrl calls run simultaneously.
   testFutures.add(client.getUrl(Uri.parse('https://$HOST_NAME:$port/$result'))
     .then((HttpClientRequest request) {
       expect(result == 'true');  // The session cache may keep the session.
+      return request.close();
     }, onError: (e) {
       expect(e is HandshakeException || e is SocketException);
     }));
 
   client.badCertificateCallback = badCertificateCallback;
   testFutures.add(client.getUrl(Uri.parse('https://$HOST_NAME:$port/$result'))
     .then((HttpClientRequest request) {
       expect(result == 'true');
-      request.close().then((result) { });
+      return request.close();
     }, onError: (e) {
       if (result == 'false') expect (e is HandshakeException ||
                                      e is SocketException);
       else if (result == 'exception') expect (e is ExpectException ||
                                               e is SocketException);
       else expect (e is ArgumentError || e is SocketException);
     }));
 
   client.badCertificateCallback = null;
   testFutures.add(client.getUrl(Uri.parse('https://$HOST_NAME:$port/$result'))
     .then((HttpClientRequest request) {
       expect(result == 'true');  // The session cache may keep the session.
+      return request.close();
     }, onError: (e) {
       expect(e is HandshakeException || e is SocketException);
     }));
 
   return Future.wait(testFutures);
 }
 
 void main() {
   final args = new Options().arguments;
   SecureSocket.initialize();
   int port = int.parse(args[0]);
   runHttpClient(port, args[1])
     .then((_) => print('SUCCESS'));
 }