Construct EstimatorSpec for EVAL mode.

def estimator_spec_eval(
      self, features, logits, labels, loss, restore_hook, use_tpu):
    """Construct EstimatorSpec for EVAL mode."""
    hparams = self.hparams
    problem = hparams.problem
    if logits.get_shape().ndims == 3:
      logits = tf.expand_dims(tf.expand_dims(logits, 2), 3)

    # Support for multiproblem
    task_list = [problem]
    if hasattr(problem, "task_list"):
      task_list = problem.task_list

    eval_metrics_fns = metrics.create_evaluation_metrics(task_list, hparams)

    if use_tpu:
      def metric_fn(tf_logits, labels):
        with tf.device("cpu:0"), mtf.utils.outside_all_rewrites():
          eval_metrics = {}
          for metric_name, metric_fn in six.iteritems(eval_metrics_fns):
            if metric_name.split("/")[-1] not in t2t_model.TPU_METRIC_BLACKLIST:
              eval_metrics[metric_name] = metric_fn(
                  tf_logits, None, tf.identity(labels))
          return eval_metrics
      return tpu_estimator.TPUEstimatorSpec(
          tf.estimator.ModeKeys.EVAL,
          evaluation_hooks=[restore_hook],
          loss=loss,
          eval_metrics=(metric_fn, [logits, labels]))
    else:
      eval_metrics = {}
      predictions = {"predictions": logits}
      for metric_name, metric_fn in six.iteritems(eval_metrics_fns):
        eval_metrics[metric_name] = metric_fn(logits, features,
                                              features["targets"])

      return tf.estimator.EstimatorSpec(
          tf.estimator.ModeKeys.EVAL,
          predictions=predictions,
          eval_metric_ops=eval_metrics,
          evaluation_hooks=[restore_hook],
          loss=loss)