Refactor Future constructors.

utils/pub/validator/utf8_readme.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 utf8_readme_validator;
 
 import 'dart:async';
 import 'dart:utf';
 
 import 'package:pathos/path.dart' as path;
 
 import '../entrypoint.dart';
 import '../io.dart';
 import '../utils.dart';
 import '../validator.dart';
 
 /// Validates that a package's README is valid utf-8.
 class Utf8ReadmeValidator extends Validator {
   Utf8ReadmeValidator(Entrypoint entrypoint)
     : super(entrypoint);
 
   Future validate() {
-    return new Future.of(() {
+    return new Future.sync(() {
       var readme = entrypoint.root.readmePath;
       if (readme == null) return;
       var bytes = readBinaryFile(readme);
       try {
         // The second and third arguments here are the default values. The
         // fourth tells [decodeUtf8] to throw an ArgumentError if `bytes` isn't
         // valid utf-8.
         decodeUtf8(bytes, 0, null, null);
       } on ArgumentError catch (_) {
         warnings.add("$readme contains invalid UTF-8.\n"
             "This will cause it to be displayed incorrectly on "
                 "pub.dartlang.org.");
       }
     });
   }
 }