Refactor Future constructors.

utils/pub/io.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.
 
 /// Helper functionality to make working with IO easier.
 library io;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
@@ skipping 530 matching lines @@
 }
 
 /// Creates a temporary directory and passes its path to [fn]. Once the [Future]
 /// returned by [fn] completes, the temporary directory and all its contents
 /// will be deleted. [fn] can also return `null`, in which case the temporary
 /// directory is deleted immediately afterwards.
 ///
 /// Returns a future that completes to the value that the future returned from
 /// [fn] completes to.
 Future withTempDir(Future fn(String path)) {
-  return new Future.of(() {
+  return new Future.sync(() {
     var tempDir = createTempDir();
-    return new Future.of(() => fn(tempDir))
+    return new Future.sync(() => fn(tempDir))
         .whenComplete(() => deleteEntry(tempDir));
   });
 }
 
 /// Extracts a `.tar.gz` file from [stream] to [destination]. Returns whether
 /// or not the extraction was successful.
 Future<bool> extractTarGz(Stream<List<int>> stream, String destination) {
   log.fine("Extracting .tar.gz stream to $destination.");
 
   if (Platform.operatingSystem == "windows") {
@@ skipping 165 matching lines @@
   const PubProcessResult(this.stdout, this.stderr, this.exitCode);
 
   bool get success => exitCode == 0;
 }
 
 /// Gets a [Uri] for [uri], which can either already be one, or be a [String].
 Uri _getUri(uri) {
   if (uri is Uri) return uri;
   return Uri.parse(uri);
 }