Validate a model's performance on a set of holdout data.

def validate(*tf_records):
    """Validate a model's performance on a set of holdout data."""
    if FLAGS.use_tpu:
        def _input_fn(params):
            return preprocessing.get_tpu_input_tensors(
                params['batch_size'], tf_records, filter_amount=1.0)
    else:
        def _input_fn():
            return preprocessing.get_input_tensors(
                FLAGS.train_batch_size, tf_records, filter_amount=1.0,
                shuffle_examples=False)

    steps = FLAGS.examples_to_validate // FLAGS.train_batch_size
    if FLAGS.use_tpu:
        steps //= FLAGS.num_tpu_cores

    estimator = dual_net.get_estimator()
    with utils.logged_timer("Validating"):
        estimator.evaluate(_input_fn, steps=steps, name=FLAGS.validate_name)