*       Executor)} instead, with a function that returns the next value directly.
   *   <li>Call {@link DeferredCloser#eventuallyClose(Object, Executor) closer.eventuallyClose()}
   *       for every closeable object this step creates in order to capture it for later closing.
   *   <li>Return a {@code ClosingFuture}. To turn a {@link ListenableFuture} into a {@code
   *       ClosingFuture} call {@link #from(ListenableFuture)}.