Handle Future result from Future.sync computation

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:async_helper/async_helper.dart';
 import "package:expect/expect.dart";
 import 'dart:async';
 
@@ skipping 599 matching lines @@
   asyncStart();
 
   future.then((v) => new Future.error("Fehler"))
         .then((v) { Expect.fail("unreachable!"); }, onError: (error) {
           Expect.equals("Fehler", error);
           asyncEnd();
         });
   completer.complete(21);
 }
 
+void testSyncFuture_i13368() {
+  asyncStart();
+
+  final future = new Future<int>.sync(() {
+      return new Future<int>.value(42);
+    });
+
+  future.then((int val) {
+      Expect.equals(val, 42);
+      asyncEnd();
+    });
+}
+
 main() {
   testValue();
   testSync();
   testNeverComplete();
 
   testComplete();
   testCompleteWithSuccessHandlerBeforeComplete();
   testCompleteWithSuccessHandlerAfterComplete();
   testCompleteManySuccessHandlers();
   testCompleteWithError();
@@ skipping 21 matching lines @@
   testFutureWhenErrorFutureError();
 
   testFutureThenThrowsAsync();
   testFutureCatchThrowsAsync();
   testFutureWhenThrowsAsync();
   testFutureCatchRethrowsAsync();
 
   testChainedFutureValue();
   testChainedFutureValueDelay();
   testChainedFutureError();
+
+  testSyncFuture_i13368();
 }