*   can call notifyFailed.)
       *
       * - ServiceDelegate.runningTask contains an instance of ReschedulableCallable (at least in
       *   the case that the service is using CustomScheduler). (It needs it so that it can cancel
       *   the task and detect whether it has been cancelled.)
       *
       * - ReschedulableCallable has a reference back to its enclosing CustomScheduler. (It needs it