Refactor Future constructors.

utils/pub/validator/compiled_dartdoc.dart

 // Copyright (c) 2012, 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 compiled_dartdoc_validator;
 
 import 'dart:async';
 
 import 'package:pathos/path.dart' as path;
 
 import '../entrypoint.dart';
 import '../io.dart';
 import '../utils.dart';
 import '../validator.dart';
 
 /// Validates that a package doesn't contain compiled Dartdoc
 /// output.
 class CompiledDartdocValidator extends Validator {
   CompiledDartdocValidator(Entrypoint entrypoint)
     : super(entrypoint);
 
   Future validate() {
-    return new Future.of(() {
+    return new Future.sync(() {
       for (var entry in listDir(entrypoint.root.dir, recursive: true)) {
         if (path.basename(entry) != "nav.json") continue;
         var dir = path.dirname(entry);
 
         // Look for tell-tale Dartdoc output files all in the same directory.
         var files = [
           entry,
           path.join(dir, "index.html"),
           path.join(dir, "styles.css"),
           path.join(dir, "dart-logo-small.png"),
           path.join(dir, "client-live-nav.js")
         ];
 
         if (files.every((val) => fileExists(val))) {
           warnings.add("Avoid putting generated documentation in "
                   "${path.relative(dir)}.\n"
               "Generated documentation bloats the package with redundant "
                   "data.");
         }
       }
     });
   }
 }