ImageToolkitForm::submitForm

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

public function submitForm(array &$form, FormStateInterface $form_state) {
  $this->config('system.image')
    ->set('toolkit', $form_state->getValue('image_toolkit'))
    ->save();

  // Call the form submit handler for each of the toolkits.
  foreach ($this->availableToolkits as $toolkit) {
    $toolkit->submitConfigurationForm($form, $form_state);
  }

  parent::submitForm($form, $form_state);
}