chromium has the ability to create desktop files that are shortcuts to websites, and it opens them in a standalone window, with a custom icon and minimal chrome (webapp mode).
Bug #1732482 tracks why this doesn’t work just yet in chromium, but with minimal changes I have managed to have it create said desktop files under
$HOME/snap/chromium/current/.local/share/applications. This is not very useful though, as gnome shell (and other desktop environments) is not expecting desktop files there (it looks in
$XDG_DATA_DIRS does the trick, but it’s just a hack. I wonder if we could devise a proper mechanism for snaps in general to expose desktop files that they create for DEs to see. Or is it a terrible idea security-wise?