Allow file scheme urls for org.chromium.UrlHandlerService

A follow up CL will modify cicerone to do path translations.
$HOME => file://media/fuse/crostini_<cryptohome-hash>_termina_penguin
/mnt/chromeos/MyFiles => /home/chronos/u-<cryptohome-hash>/MyFiles
/mnt/chromeos/GoogleDrive => /media/fuse/drivefs-<drivefs-hash>
/mnt/chromeos/PlayFiles => /run/arc/sdcard/write/emulated/0
other: Not visible and cicerone will fail before sending.

Bug: 908122
Change-Id: I566021713541edf4a849cf93ced8c315bb4a87c4
Reviewed-on: https://chromium-review.googlesource.com/c/1401924
Reviewed-by: Nicholas Verne <nverne@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621304}
1 file changed