Submit handler to add a display to a view.
public function submitDisplayAdd($form, &$form_state) {
$view = $this->entity;
// Create the new display.
$parents = $form_state['triggering_element']['#parents'];
$display_type = array_pop($parents);
$display_id = $view
->addDisplay($display_type);
// A new display got added so the asterisks symbol should appear on the new
// display.
$view
->get('executable')->current_display = $display_id;
$view
->cacheSet();
// Redirect to the new display's edit page.
$form_state['redirect'] = 'admin/structure/views/view/' . $view
->id() . '/edit/' . $display_id;
}