Refactor Future constructors.

utils/pub/hosted_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 hosted_source;
 
 import 'dart:async';
 import 'dart:io' as io;
 import 'dart:json' as json;
 import 'dart:uri';
@@ skipping 45 matching lines @@
     return httpClient.read(url).then((yaml) {
       return new Pubspec.parse(null, yaml, systemCache.sources);
     }).catchError((ex) {
       var parsed = _parseDescription(id.description);
       _throwFriendlyError(ex, id, parsed.last);
     });
   }
 
   /// Downloads a package from the site and unpacks it.
   Future<bool> install(PackageId id, String destPath) {
-    return new Future.of(() {
+    return new Future.sync(() {
       var url = _makeVersionUrl(id, (server, package, version) =>
           "$server/packages/$package/versions/$version.tar.gz");
       log.io("Install package from $url.");
 
       log.message('Downloading $id...');
 
       // Download and extract the archive to a temp directory.
       var tempDir = systemCache.createTempDir();
       return httpClient.send(new http.Request("GET", url))
           .then((response) => response.stream)
@@ skipping 14 matching lines @@
   /// for each separate repository URL that's used on the system. Each of these
   /// subdirectories then contains a subdirectory for each package installed
   /// from that site.
   Future<String> systemCacheDirectory(PackageId id) {
     var parsed = _parseDescription(id.description);
     var url = _getSourceDirectory(parsed.last);
     var urlDir = replace(url, new RegExp(r'[<>:"\\/|?*%]'), (match) {
       return '%${match[0].codeUnitAt(0)}';
     });
 
-    return new Future.immediate(
+    return new Future.value(
         path.join(systemCacheRoot, urlDir, "${parsed.first}-${id.version}"));
   }
 
   String packageName(description) => _parseDescription(description).first;
 
   bool descriptionsEqual(description1, description2) =>
       _parseDescription(description1) == _parseDescription(description2);
 
   /// Ensures that [description] is a valid hosted package description.
   ///
@@ skipping 88 matching lines @@
   }
 
   var name = description["name"];
   if (name is! String) {
     throw new FormatException("The 'name' key must have a string value.");
   }
 
   var url = description.containsKey("url") ? description["url"] : _defaultUrl;
   return new Pair<String, String>(name, url);
 }