...in favor of just calling `setException` unconditionally.

I wrote in a code review:

> There's a decent argument that the work we do here and in MoreExecutors.rejectionPropagatingExecutor isn't really buying us much, since it's not clear where else a RejectedExecutionException would be coming from. And even if it is coming from somewhere else, the most plausible location of all the implausible locations is "somewhere after we already called set/setException/setFuture/cancel," in which case we could still call setException(), confident in the knowledge that it will be a no-op.
> 
> Or maybe I'm forgetting something important. Beats me :) But certainly it's hard (impossible?) to write a test that covers this case.
}
    @Override
    public ListenableScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
      TrustedListenableFutureTask<Void> task = TrustedListenableFutureTask.create(command, null);
      ScheduledFuture<?> scheduled = delegate.schedule(task, delay, unit);
      return new ListenableScheduledTask<>(task, scheduled);
    }
    @Override
    public <V> ListenableScheduledFuture<V> schedule(
        Callable<V> callable, long delay, TimeUnit unit) {
      TrustedListenableFutureTask<V> task = TrustedListenableFutureTask.create(callable);
      ScheduledFuture<?> scheduled = delegate.schedule(task, delay, unit);
      return new ListenableScheduledTask<V>(task, scheduled);
    }
    @Override
    public ListenableScheduledFuture<?> scheduleAtFixedRate(
        Runnable command, long initialDelay, long period, TimeUnit unit) {
      NeverSuccessfulListenableFutureTask task = new NeverSuccessfulListenableFutureTask(command);
      ScheduledFuture<?> scheduled = delegate.scheduleAtFixedRate(task, initialDelay, period, unit);
      return new ListenableScheduledTask<>(task, scheduled);
    }
    @Override
    public ListenableScheduledFuture<?> scheduleWithFixedDelay(
        Runnable command, long initialDelay, long delay, TimeUnit unit) {
      NeverSuccessfulListenableFutureTask task = new NeverSuccessfulListenableFutureTask(command);
      ScheduledFuture<?> scheduled =
          delegate.scheduleWithFixedDelay(task, initialDelay, delay, unit);
      return new ListenableScheduledTask<>(task, scheduled);
    }
    private static final class ListenableScheduledTask<V>