NodeRevisionRevertForm::submitForm

public NodeRevisionRevertForm::submitForm(array &$form, FormStateInterface $form_state)

public function submitForm(array &$form, FormStateInterface $form_state) {
  // The revision timestamp will be updated when the revision is saved. Keep
  // the original one for the confirmation message.
  $original_revision_timestamp = $this->revision->getRevisionCreationTime();

  $this->revision = $this->prepareRevertedRevision($this->revision, $form_state);
  $this->revision->revision_log = t('Copy of the revision from %date.', ['%date' => $this->dateFormatter->format($original_revision_timestamp)]);
  $this->revision->save();

  $this->logger('content')->notice('@type: reverted %title revision %revision.', ['@type' => $this->revision->bundle(), '%title' => $this->revision->label(), '%revision' => $this->revision->getRevisionId()]);
  drupal_set_message(t('@type %title has been reverted to the revision from %revision-date.', ['@type' => node_get_type_label($this->revision), '%title' => $this->revision->label(), '%revision-date' => $this->dateFormatter->format($original_revision_timestamp)]));
  $form_state->setRedirect(
  'entity.node.version_history', 
  array('node' => $this->revision->id())
  );
}