Given two node IDs, return all the pooling layers between them.

def _get_pooling_layers(self, start_node_id, end_node_id):
        """Given two node IDs, return all the pooling layers between them."""
        layer_list = []
        node_list = [start_node_id]
        assert self._depth_first_search(end_node_id, layer_list, node_list)
        ret = []
        for layer_id in layer_list:
            layer = self.layer_list[layer_id]
            if is_layer(layer, "Pooling"):
                ret.append(layer)
            elif is_layer(layer, "Conv") and layer.stride != 1:
                ret.append(layer)
        return ret