Evaluate until checkpoints stop being produced.

def continuous_eval(self):
    """Evaluate until checkpoints stop being produced."""
    for ckpt_path in next_checkpoint(self._hparams.model_dir,
                                     self._hparams.eval_timeout_mins):
      # Skip zero'th step.
      train_step = decoding.get_step_from_ckpt_path(ckpt_path)
      if train_step == 0:
        tf.logging.info("Skipping evaluation at step 0")
        continue
      self.evaluate()