/**
   * Submit handler for tab.
   */
  public function tabSave($form, FormStateInterface $form_state) {
    $this->save($form, $form_state);

    // Check if this field has any configuration options.
    $tab = $this->tabManager->getDefinition($form_state->getValue('new'));

    // Load the configuration form for this option.
    if (is_subclass_of($tab['class'], '\Drupal\blocktabs\ConfigurableTabInterface')) {
      $form_state->setRedirect(
        'blocktabs.tab_add_form',
        array(
          'blocktabs' => $this->entity->id(),
          'tab' => $form_state->getValue('new'),
        ),
        array('query' => array('weight' => $form_state->getValue('weight')))
      );
    }
    // If there's no form, immediately add the tab.
    else {
      $tab = array(
        'id' => $tab['id'],
        'data' => array(),
        'weight' => $form_state->getValue('weight'),
      );
      $tab_id = $this->entity->addTab($tab);
      $this->entity->save();
      if (!empty($tab_id)) {
        drupal_set_message($this->t('The tab was successfully added.'));
      }
    }
  }
 /**
  * {@inheritdoc}
  */
 protected function prepareTab($tab) {
   $tab = $this->tabManager->createInstance($tab);
   // Set the initial weight so this tab comes last.
   $tab->setWeight(count($this->blocktabs->getTabs()));
   return $tab;
 }