Fix Chrome not launching in fullscreen

On my system, if you use --app, Chromium launches as a small window,
even when --kiosk is specified. By launching it as a URL instead of
using --app, it correctly opens in kiosk mode.

It's worth noting that --window_size does not let it work correctly
either, as the browser launches in windowed mode instead of fullscreen.

All testing has been performed with YouTube.