Refactor Future constructors.

utils/pub/git_source.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 git_source;
 
 import 'dart:async';
 
 import 'package:pathos/path.dart' as path;
 
@@ skipping 105 matching lines @@
     });
   }
 
   // TODO(keertip): Implement getCachedPackages().
   
   /// Ensure that the canonical clone of the repository referred to by [id] (the
   /// one in `<system cache>/git/cache`) exists and is up-to-date. Returns a
   /// future that completes once this is finished and throws an exception if it
   /// fails.
   Future _ensureRepoCache(PackageId id) {
-    return new Future.of(() {
+    return new Future.sync(() {
       var path = _repoCachePath(id);
       if (!entryExists(path)) return _clone(_getUrl(id), path, mirror: true);
       return git.run(["fetch"], workingDir: path).then((result) => null);
     });
   }
 
   /// Returns a future that completes to the revision hash of [id].
   Future<String> _revisionAt(PackageId id) {
     return git.run(["rev-parse", _getEffectiveRef(id)],
         workingDir: _repoCachePath(id)).then((result) => result[0]);
   }
 
   /// Clones the repo at the URI [from] to the path [to] on the local
   /// filesystem.
   ///
   /// If [mirror] is true, create a bare, mirrored clone. This doesn't check out
   /// the working tree, but instead makes the repository a local mirror of the
   /// remote repository. See the manpage for `git clone` for more information.
   Future _clone(String from, String to, {bool mirror: false}) {
-    return new Future.of(() {
+    return new Future.sync(() {
       // Git on Windows does not seem to automatically create the destination
       // directory.
       ensureDir(to);
       var args = ["clone", from, to];
       if (mirror) args.insert(1, "--mirror");
       return git.run(args);
     }).then((result) => null);
   }
 
   /// Checks out the reference [ref] in [repoPath].
@@ skipping 45 matching lines @@
     return description['ref'];
   }
 
   /// Returns [description] if it's a description, or [PackageId.description] if
   /// it's a [PackageId].
   _getDescription(description) {
     if (description is PackageId) return description.description;
     return description;
   }
 }