Getting the header(or a custom block) for API use

Question

I want to generate the header and serve it via API for displaying outside of the Magento website.

I've found a working example for Magento 1 but I couldn't figure out how to do it for Magento 2.

/*
         * Add specific layout handles to our layout and then load them.
         */
        $layout = Mage::app()->getLayout();
        $layout->getUpdate()
            ->addHandle('default')
            ->addHandle('ixcbadv_header')
            ->addHandle('facebook');

        if ($magento_logged_in) {
            $layout->getUpdate()->addHandle('customer_logged_in');
        } else {
            $layout->getUpdate()->addHandle('customer_logged_out');
        }

        $magento_google_analytics = $layout->createBlock('googleanalytics/ga')->setTemplate('googleanalytics/ga.phtml')->toHtml();

        $layout->getUpdate()->load();

        /*
         * Generate blocks, but XML from previously loaded layout handles must be
         * loaded first.
         */
        $layout->generateXml()->generateBlocks();

Any ideas? Thanks!