Bottleneck residual unit with 3 sub layers.

def _bottleneck_residual(self, x, in_filter, out_filter, stride,
                           activate_before_residual=False):
    """Bottleneck residual unit with 3 sub layers."""
    if activate_before_residual:
      with tf.variable_scope('common_bn_relu'):
        x = self._layer_norm('init_bn', x)
        x = self._relu(x, self.hps.relu_leakiness)
        orig_x = x
    else:
      with tf.variable_scope('residual_bn_relu'):
        orig_x = x
        x = self._layer_norm('init_bn', x)
        x = self._relu(x, self.hps.relu_leakiness)

    with tf.variable_scope('sub1'):
      x = self._conv('conv1', x, 1, in_filter, out_filter / 4, stride)

    with tf.variable_scope('sub2'):
      x = self._layer_norm('bn2', x)
      x = self._relu(x, self.hps.relu_leakiness)
      x = self._conv('conv2', x, 3, out_filter / 4,
                     out_filter / 4, [1, 1, 1, 1])

    with tf.variable_scope('sub3'):
      x = self._layer_norm('bn3', x)
      x = self._relu(x, self.hps.relu_leakiness)
      x = self._conv('conv3', x, 1, out_filter /
                     4, out_filter, [1, 1, 1, 1])

    with tf.variable_scope('sub_add'):
      if in_filter != out_filter:
        orig_x = self._conv('project', orig_x, 1,
                            in_filter, out_filter, stride)
      x += orig_x

    return x