Refactor Future constructors.

utils/pub/git.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.
 
 /// Helper functionality for invoking Git.
 library git;
 
 import 'dart:async';
 import 'io.dart';
 import 'log.dart' as log;
 import 'utils.dart';
 
 /// Tests whether or not the git command-line app is available for use.
 Future<bool> get isInstalled {
   if (_isGitInstalledCache != null) {
-    return new Future.immediate(_isGitInstalledCache);
+    return new Future.value(_isGitInstalledCache);
   }
 
   return _gitCommand.then((git) => git != null);
 }
 
 /// Run a git process with [args] from [workingDir]. Returns the stdout as a
 /// list of strings if it succeeded. Completes to an exception if it failed.
 Future<List<String>> run(List<String> args,
     {String workingDir, Map<String, String> environment}) {
   return _gitCommand.then((git) {
@@ skipping 10 matching lines @@
 
 bool _isGitInstalledCache;
 
 /// The cached Git command.
 String _gitCommandCache;
 
 /// Returns the name of the git command-line app, or null if Git could not be
 /// found on the user's PATH.
 Future<String> get _gitCommand {
   if (_gitCommandCache != null) {
-    return new Future.immediate(_gitCommandCache);
+    return new Future.value(_gitCommandCache);
   }
 
   return _tryGitCommand("git").then((success) {
     if (success) return "git";
 
     // Git is sometimes installed on Windows as `git.cmd`
     return _tryGitCommand("git.cmd").then((success) {
       if (success) return "git.cmd";
       return null;
     });
   }).then((command) {
     log.fine('Determined git command $command.');
     _gitCommandCache = command;
     return command;
   });
 }
 
 /// Checks whether [command] is the Git command for this computer.
 Future<bool> _tryGitCommand(String command) {
   // If "git --version" prints something familiar, git is working.
   return runProcess(command, ["--version"]).then((results) {
     var regexp = new RegExp("^git version");
     return results.stdout.length == 1 && regexp.hasMatch(results.stdout[0]);
   }).catchError((err) {
     // If the process failed, they probably don't have it.
     return false;
   });
 }