Add built-in timeouts to scheduled_test.

pkg/scheduled_test/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 utils;
 
 import 'dart:async';
 
 /// Configures [future] so that its result (success or exception) is passed on
 /// to [completer].
 void chainToCompleter(Future future, Completer completer) {
   future.then((value) => completer.complete(value),
       onError: (e) => completer.completeError(e.error, e.stackTrace));
 }
 
 /// Prepends each line in [text] with [prefix].
 String prefixLines(String text, {String prefix: '| '}) =>
   text.split('\n').map((line) => '$prefix$line').join('\n');
+
+/// Returns a [Future] that completes after pumping the event queue [times]
+/// times. By default, this should pump the event queue enough times to allow
+/// any code to run, as long as it's not waiting on some external event.
+Future pumpEventQueue([int times=200]) {
+  if (times == 0) return new Future.immediate(null);
+  return new Future.immediate(null).then((_) => pumpEventQueue(times - 1));
+}