Form submission handler for the Preview button.
public function submitPreview($form, &$form_state) {
// Rebuild the form with a pristine $view object.
$view = $this
->getEntity($form_state);
$form_state['build_info']['args'][0] = views_ui_cache_load($view
->get('name'));
$view->renderPreview = TRUE;
$form_state['show_preview'] = TRUE;
$form_state['rebuild'] = TRUE;
}