anchor.diff:  
     Completer get completer => _completer;
   
  -  Future get future => _completer.future;
  +  Future<SparkJobStatus> get future => _completer.future;
   
     Job(this.name, [Completer completer]) {
       if (completer != null) {
         _completer = completer;
       } else {
  -      _completer = new Completer();
  +      _completer = new Completer<SparkJobStatus>();
       }
     }
   
  
positive.code:    * Will schedule a [job] after all other queued jobs. If no [Job] is currently
     * waiting, [job] will run.
     */
    Future schedule(Job job) {
      Completer completer = job.completer;
      _waitingJobs.add(job);
  
  
negative.code: 
    ProgressJob(String name, Completer completer) : super(name, completer);
  
    Future<SparkJobStatus> run(ProgressMonitor monitor) {
      monitor.start(name);
      return _completer.future;
    }
  