Пояснение:
При запуске примера - стартер кит приложения, добавлял дополнительную страницу на сайт.
Ниже такая фраза:
Register the page for the build
When you deploy your application to the web, you'll use the Polymer CLI to prepare your files for deployment. Polymer CLI will need to know about any DEMAND-LOADED fragments like the lazy-loaded view you just added.
