BlockContentForm::save

public BlockContentForm::save(array $form, FormStateInterface $form_state)

public function save(array $form, FormStateInterface $form_state) {
  $block = $this->entity;

  // Save as a new revision if requested to do so.
  if (!$form_state->isValueEmpty('revision')) {
    $block->setNewRevision();
    // If a new revision is created, save the current user as revision author.
    $block->setRevisionCreationTime(REQUEST_TIME);
    $block->setRevisionUserId(\Drupal::currentUser()->id());
  }

  $insert = $block->isNew();
  $block->save();
  $context = array('@type' => $block->bundle(), '%info' => $block->label());
  $logger = $this->logger('block_content');
  $block_type = $this->blockContentTypeStorage->load($block->bundle());
  $t_args = array('@type' => $block_type->label(), '%info' => $block->label());

  if ($insert) {
    $logger->notice('@type: added %info.', $context);
    drupal_set_message($this->t('@type %info has been created.', $t_args));
  }
  else {
    $logger->notice('@type: updated %info.', $context);
    drupal_set_message($this->t('@type %info has been updated.', $t_args));
  }

  if ($block->id()) {
    $form_state->setValue('id', $block->id());
    $form_state->set('id', $block->id());
    if ($insert) {
      if (!$theme = $block->getTheme()) {
        $theme = $this->config('system.theme')->get('default');
      }
      $form_state->setRedirect(
      'block.admin_add', 
      array(
        'plugin_id' => 'block_content:' . $block->uuid(),
        'theme' => $theme,
      )
      );
    }
    else {
      $form_state->setRedirectUrl($block->urlInfo('collection'));
    }
  }
  else {
    // In the unlikely case something went wrong on save, the block will be
    // rebuilt and block form redisplayed.
    drupal_set_message($this->t('The block could not be saved.'), 'error');
    $form_state->setRebuild();
  }
}