Returns total size (in bytes) of the given 'directory'.

def _dir_size(directory):
  """Returns total size (in bytes) of the given 'directory'."""
  size = 0
  for elem in tf_v1.gfile.ListDirectory(directory):
    elem_full_path = os.path.join(directory, elem)
    stat = tf_v1.gfile.Stat(elem_full_path)
    size += _dir_size(elem_full_path) if stat.is_directory else stat.length
  return size