Tuple of `tf.TensorShape`s indicating the size of state tensors.

def state_size(self):
    """Tuple of `tf.TensorShape`s indicating the size of state tensors."""
    if self._max_unique_stats == 1:
      return (tf.TensorShape([self._hidden_size]),
              tf.TensorShape([self._hidden_size]))
    else:
      return (tf.TensorShape([self._hidden_size]),
              tf.TensorShape([self._hidden_size]),
              tf.TensorShape(1))