Refactor Future constructors.

utils/pub/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 source;
 
 import 'dart:async';
 
 import 'package:pathos/path.dart' as path;
 
@@ skipping 136 matching lines @@
     // If we got here, it's OK.
     return false;
   }
 
   /// Returns the directory in the system cache that the package identified by
   /// [id] should be installed to. This should return a path to a subdirectory
   /// of [systemCacheRoot].
   ///
   /// This doesn't need to be implemented if [shouldCache] is false.
   Future<String> systemCacheDirectory(PackageId id) {
-    return new Future.immediateError(
+    return new Future.error(
         "systemCacheDirectory() must be implemented if shouldCache is true.");
   }
 
   /// When a [Pubspec] or [LockFile] is parsed, it reads in the description for
   /// each dependency. It is up to the dependency's [Source] to determine how
   /// that should be interpreted. This will be called during parsing to validate
   /// that the given [description] is well-formed according to this source, and
   /// to give the source a chance to canonicalize the description.
   ///
   /// [containingPath] is the path to the local file (pubspec or lockfile)
@@ skipping 31 matching lines @@
   /// This will be called after the package identified by [id] is installed, so
   /// the source can use the installed package to determine information about
   /// the resolved id.
   ///
   /// The returned [PackageId] may have a description field that's invalid
   /// according to [parseDescription], although it must still be serializable
   /// to JSON and YAML. It must also be equal to [id] according to
   /// [descriptionsEqual].
   ///
   /// By default, this just returns [id].
-  Future<PackageId> resolveId(PackageId id) => new Future.immediate(id);
+  Future<PackageId> resolveId(PackageId id) => new Future.value(id);
   
   /// Returns the [Package]s that have been installed in the system cache.
   List<Package> getCachedPackages() {
     if (shouldCache) throw "Source $name must implement this.";
   }
 
   /// Returns the source's name.
   String toString() => name;
 }