Issue #3222844 by guilhermevp, paulocs, dhirendra.mishra, joachim, quietone,...

  /**

   * Performs an import operation - migrate items from source to destination.

   *

   * @return int

   *   Returns a value indicating the status of the import operation.

   *   The possible values are the 'RESULT_' constants defined

   *   in MigrationInterface.

   *

   * @see \Drupal\migrate\Plugin\MigrationInterface

   */

  public function import();