Refactor Future constructors.

pkg/http/test/multipart_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.
 
 library multipart_test;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:utf';
 
@@ skipping 195 matching lines @@
 
   group('in a temp directory', () {
     var tempDir;
     setUp(() {
       tempDir = new Directory('').createTempSync();
     });
 
     tearDown(() => tempDir.deleteSync(recursive: true));
 
     test('with a file from disk', () {
-      expect(new Future.of(() {
+      expect(new Future.sync(() {
         var filePath = path.join(tempDir.path, 'test-file');
         new File(filePath).writeAsStringSync('hello');
         return http.MultipartFile.fromPath('file', filePath);
       }).then((file) {
         var request = new http.MultipartRequest('POST', dummyUrl);
         request.files.add(file);
 
         expect(request, bodyMatches('''
         --{{boundary}}
         content-type: application/octet-stream
         content-disposition: form-data; name="file"; filename="test-file"
 
         hello
         --{{boundary}}--
         '''));
       }), completes);
     });
   });
 }