One reason for adding this is to make Chromium able to open files it has
downloaded.
Currently this happens:
/run/current-system/sw/bin/xdg-open: line 364: gnome-open: command not found
(And nothing happens in the GUI when clicking a downloaded file.)
Looking into xdg-open, one can see that it first tries to run gvfs-open
and then falls back to gnome-open. Adding 'gvfs' makes the first command
succeed.
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