/**
   * Implements MapperInterface::getPluginType().
   */
  function getPluginType($scope, $type, $config_class = 'Drupal\Config\DrupalConfig') {
    if (empty($this->configuration[$scope][$type])) {
      $this->configuration[$scope][$type] = config("plugin.type.$scope.$type", $config_class);
    }
    return $this->configuration[$scope][$type];
  }

// Config does this last I looked:

function config($name, $class = 'Drupal\Config\DrupalConfig') {
  // @todo Replace this with an appropriate factory.
  return new $class(new DrupalVerifiedStorageSQL($name));
}