For those doing client work, you're going to get asked:
"The new popup isn't going to work on every site. Chrome's implementation will only work for sites that offer an app-like experience. Google requires that sites serve themselves in HTTPS, have a service worker on the site, and use the WebApp manifest."
http://arstechnica.com/gadgets/2015/03/chrome-for-android-to-push-web-app-adoption-with-add-to-home-screen-popup/