Submit handler to convert an overridden style to its default.
function image_style_revert_form_submit($form, &$form_state) {
drupal_set_message(t('The %style style has been reverted to its defaults.', array(
'%style' => $form_state['image_style']['label'],
)));
image_default_style_revert($form_state['image_style']);
$form_state['redirect'] = 'admin/config/media/image-styles';
}