class FieldUI

FieldEditForm.php in drupal/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php

Contains \Drupal\field_ui\Form\FieldEditForm.

FieldInstanceFormBase.php in drupal/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldInstanceFormBase.php

Contains \Drupal\field_ui\Form\FieldInstanceFormBase.

class FieldUI {

  /**
   * Returns the next redirect path in a multipage sequence.
   *
   * @return array
   *   An array of redirect paths.
   */
  public static function getNextDestination() {
    $next_destination = array();
    $destinations = !empty($_REQUEST['destinations']) ? $_REQUEST['destinations'] : array();
    if (!empty($destinations)) {
      unset($_REQUEST['destinations']);
      $path = array_shift($destinations);
      $options = drupal_parse_url($path);
      if ($destinations) {
        $options['query']['destinations'] = $destinations;
      }
      $next_destination = array(
        $options['path'],
        $options,
      );
    }
    return $next_destination;
  }

}