Make Completers asynchronous.

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 "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:isolate';
 
@@ skipping 58 matching lines @@
 
   future.then((v) => Expect.equals(3, v));
 }
 
 // Tests for [then]
 
 testCompleteWithSuccessHandlerBeforeComplete() {
   final completer = new Completer<int>();
   final future = completer.future;
 
-  int value;
-  future.then((int v) { value = v; });
-  Expect.isNull(value);
+  int after;
 
-  Expect.isFalse(completer.isCompleted);
+  var port = new ReceivePort();
+  future.then((int v) { after = v; })
+    .then((_) {
+      Expect.equals(3, after);
+      port.close();
+    });
+
   completer.complete(3);
-  Expect.isTrue(completer.isCompleted);
-
-  Expect.equals(3, value);
+  Expect.isNull(after);
 }
 
 testCompleteWithSuccessHandlerAfterComplete() {
   final completer = new Completer<int>();
   final future = completer.future;
 
   int after;
   completer.complete(3);
   Expect.isNull(after);
 
@@ skipping 553 matching lines @@
   testFutureCatchThrowsAsync();
   testFutureWhenThrowsAsync();
   testFutureCatchRethrowsAsync();
 
   testChainedFutureValue();
   testChainedFutureValueDelay();
   testChainedFutureError();
 }