Prints an empty page.
This function is used to print out a bare minimum empty page which still has the scripts and styles necessary in order to trigger the overlay to close.
It can be used to prevent a page request which closes the overlay (for example, a form submission) from being fully re-rendered before the overlay is closed, thereby allowing the dialog to be closed faster and with less interruption, and also allowing the display of messages to be deferred to the parent window (rather than displaying them in the child window, which will close before the user has had a chance to read them).
\Symfony\Component\HttpFoundation\Response A Response object.
function overlay_deliver_empty_page() {
$empty_page = '<html><head><title></title>' . drupal_get_css() . drupal_get_js() . '</head><body class="overlay"></body></html>';
return new Response($empty_page);
}