Remove calls to [new Future] work around issue 11911.

pkg/barback/lib/src/utils.dart

 // Copyright (c) 2013, 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 barback.utils;
 
 import 'dart:async';
 
 /// Converts a number in the range [0-255] to a two digit hex string.
 ///
@@ skipping 83 matching lines @@
 /// any code to run, as long as it's not waiting on some external event.
 Future pumpEventQueue([int times=20]) {
   if (times == 0) return new Future.value();
   // We use a delayed future to allow runAsync events to finish. The
   // Future.value or Future() constructors use runAsync themselves and would
   // therefore not wait for runAsync callbacks that are scheduled after invoking
   // this method.
   return new Future.delayed(Duration.ZERO, () => pumpEventQueue(times - 1));
 }
 
+/// Like [new Future], but avoids issue 11911 by using [new Future.value] under
+/// the covers.
+Future newFuture(callback()) => new Future.value().then((_) => callback());