Move system performance settings from variable to config.
function system_update_8017() {
update_variables_to_config('system.performance', array(
'cache' => 'cache.page.use_internal',
'page_cache_maximum_age' => 'cache.page.max_age',
'page_compression' => 'response.gzip',
'preprocess_css' => 'css.preprocess',
'preprocess_js' => 'js.preprocess',
'stale_file_threshold' => 'stale_file_threshold',
));
}