Get rid of unneeded Future.immediate() calls.

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 'git.dart' as git;
 import 'io.dart';
 import 'package.dart';
@@ skipping 31 matching lines @@
             "Please ensure Git is correctly installed.");
       }
 
       return ensureDir(join(systemCacheRoot, 'cache'));
     }).then((_) => _ensureRepoCache(id))
       .then((_) => _revisionCachePath(id))
       .then((path) {
       revisionCachePath = path;
       return exists(revisionCachePath);
     }).then((exists) {
-      if (exists) return new Future.immediate(null);
+      if (exists) return;
       return _clone(_repoCachePath(id), revisionCachePath, mirror: false);
     }).then((_) {
       var ref = _getEffectiveRef(id);
-      if (ref == 'HEAD') return new Future.immediate(null);
+      if (ref == 'HEAD') return;
       return _checkOut(revisionCachePath, ref);
     }).then((_) {
       return Package.load(id.name, revisionCachePath, systemCache.sources);
     });
   }
 
   /// Ensures [description] is a Git URL.
   void validateDescription(description, {bool fromLockFile: false}) {
     // A single string is assumed to be a Git URL.
     if (description is String) return;
@@ skipping 124 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;
   }
 }