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This will be used at least in tast tests where the UI is used to
uninstall crostini, but the test must wait until uninstall completes
and receives result.

Bug: 849438
Change-Id: Ia44dfa80cae957082bc1641bc5540f69b0ba3b40
Reviewed-on: https://chromium-review.googlesource.com/1236616Reviewed-by: Nicholas Verne <nverne@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593056}