Change Future.delayed to take a Duration.

tests/lib/async/future_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.
 
 library future_test;
 
 import 'dart:async';
 import 'dart:isolate';
 
 const Duration MS = const Duration(milliseconds: 1);
@@ skipping 546 matching lines @@
           port.close();
         });
   completer.complete(21);
 }
 
 testChainedFutureValueDelay() {
   final completer = new Completer();
   final future = completer.future;
   var port = new ReceivePort();
 
-  future.then((v) => new Future.delayed(10, () => v * 2))
+  future.then((v) => new Future.delayed(const Duration(milliseconds: 10),
+                                        () => v * 2))
         .then((v) {
           Expect.equals(42, v);
           port.close();
         });
   completer.complete(21);
 }
 
 testChainedFutureError() {
   final completer = new Completer();
   final future = completer.future;
@@ skipping 44 matching lines @@
   testFutureCatchThrowsAsync();
   testFutureWhenThrowsAsync();
   testFutureCatchRethrowsAsync();
 
   testChainedFutureValue();
   testChainedFutureValueDelay();
   testChainedFutureError();
 }