Loads metrics for this epoch if they have already been written.

  This reads the entire event file but it's small with just per-epoch metrics.

  Args:
    event_dir: TODO(koz4k): Document this.
    epoch: TODO(koz4k): Document this.

  Returns:
    metrics.

def load_metrics(event_dir, epoch):
  """Loads metrics for this epoch if they have already been written.

  This reads the entire event file but it's small with just per-epoch metrics.

  Args:
    event_dir: TODO(koz4k): Document this.
    epoch: TODO(koz4k): Document this.

  Returns:
    metrics.
  """
  metrics = {}
  for filename in tf.gfile.ListDirectory(event_dir):
    path = os.path.join(event_dir, filename)
    for event in tf.train.summary_iterator(path):
      if event.step == epoch and event.HasField("summary"):
        value = event.summary.value[0]
        metrics[value.tag] = value.simple_value
  return metrics