Refactor Future constructors.

tests/standalone/io/directory_fuzz_test.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.
 
 // 'fuzz' test the directory APIs by providing unexpected type
 // arguments. The test passes if the VM does not crash.
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
@@ skipping 33 matching lines @@
     futures.add(doItAsync(d.create));
     futures.add(doItAsync(d.delete));
     futures.add(doItAsync(() {
       return d.createTemp().then((temp) {
         return temp.delete();
       });
     }));
     futures.add(doItAsync(() {
       return d.exists().then((res) {
         if (!res) return d.delete(recursive: true);
-        return new Future.immediate(true);
+        return new Future.value(true);
       });
     }));
     typeMapping.forEach((k2, v2) {
       futures.add(doItAsync(() => d.rename(v2)));
       futures.add(doItAsync(() {
         d.list(recursive: v2).listen((_) {}, onError: (e) => null);
       }));
     });
   });
   Future.wait(futures).then((ignore) => port.close());
 }
 
 main() {
   fuzzSyncMethods();
   fuzzAsyncMethods();
 }