CrOS FilesApp:  Allow share drive computer volumes with crostini

We currently have COMPUTERS_GRAND_ROOT as a sharable volume, but
once you drill into a specific Drive Computer, the volume is COMPUTER.

Bug: 878324
Change-Id: I25a4bf377200b37c9e5914ad558a3596484f4915
Reviewed-on: https://chromium-review.googlesource.com/c/1300354
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603004}
2 files changed