hookDisplayAdminProductsExtra

[Rodrigo B Laurindo]

I am trying to add a new tab in products edit page in back office using hook DisplayAdminProductsExtra:

public function hookDisplayAdminProductsExtra($params) {
    if (Validate::isLoadedObject($product = new Product((int)Tools::getValue('id_product'))))
    {
       return $this->renderAdminProductsExtraTab($product);
    }
}

And

  function renderAdminProductsExtraTab($product = 0)
  {   
		$fields_form_1 = array(
			'form' => array(
				'legend' => array(
					'title' => $this->l('Regras do Visual Correios para frete'),
					'icon' => 'icon-cogs'
				),
				'input' => array(
					array(
						'label' => $this->l('My field'),
						'type' => 'text',
						'name' => 'myfield',
					),
				),
			'submit' => array(
				'title' => $this->l('Save'),
				'class' => 'btn btn-default pull-right',
				'name' => 'submitEditExtraTab',
				)
 			),
		);

		$helper = new HelperForm();
		$helper->show_toolbar = false;
                $helper->table =  $this->name;
		$lang = new Language((int)Configuration::get('PS_LANG_DEFAULT'));
		$helper->default_form_language = $lang->id;
		$helper->module = $this;
		$helper->allow_employee_form_lang = Configuration::get('PS_BO_ALLOW_EMPLOYEE_FORM_LANG') ? Configuration::get('PS_BO_ALLOW_EMPLOYEE_FORM_LANG') : 0;
		$helper->identifier = $this->identifier;
		$helper->submit_action = 'submitEditExtraTab';
		$helper->currentIndex = $this->context->link->getAdminLink('AdminProducts', false);
		$helper->token = Tools::getAdminTokenLite('AdminProducts');
	        $helper->toolbar_btn = array(
                    'save' =>
                         array(
                               'short' => 'Save',
                               'desc' => $this->l('Save'),
                               'href' => AdminController::$currentIndex,
                        ),
                );	
		$helper->tpl_vars = array(
			'fields_value' => $this->getExtraTabFieldsValues($product->id),
			'languages' => $this->context->controller->getLanguages(),
			'id_language' => $this->context->language->id
		);

		return $helper->generateForm(array($fields_form_1));
  }

This code works, but it shows only a Save button. How can I get "Cancel" and "Save and stay" buttons as in other product tabs?