pkg/http_server: fixes for unittest deprecations

pkg/http_server/test/virtual_directory_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 'dart:async';
 import 'dart:io';
 
 import "package:http_server/http_server.dart";
 import 'package:path/path.dart' as pathos;
 import "package:unittest/unittest.dart";
@@ skipping 175 matching lines @@
           .then((result) {
             expect(result, 'index file');
           });
       });
 
       testVirtualDir('index-2', (dir) {
         new Directory('${dir.path}/dir').createSync();
         var virDir = new VirtualDirectory(dir.path);
         virDir.allowDirectoryListing = true;
 
-        virDir.directoryHandler = protectAsync2((dir2, request) {
+        virDir.directoryHandler = (dir2, request) {
           fail('not expected');
-        });
+        };
 
         return getStatusCodeForVirtDir(virDir, '/dir', followRedirects: false)
           .then((result) {
             expect(result, 301);
           });
       });
 
       testVirtualDir('index-3', (dir) {
         new File('${dir.path}/dir/index.html')
             ..createSync(recursive: true)
@@ skipping 321 matching lines @@
           return virDir.serveFile(new File('${d.path}/file'), request);
         };
 
         return getAsString(virDir, '/')
           .then((result) {
             expect(result, 'file contents');
           });
     });
   });
 }