update_engine: UM: UpdateCheckAllowed returns target version prefix.
This piece of information is also provided by the device policy and
needed when performing the update check. Borrows logic currently in
UpdateAttempter::CalculateUpdateParams().
BUG=chromium:358269
TEST=Unit tests.
Change-Id: I5259404df1763be8944b445d51e1fafbca946306
Reviewed-on: https://chromium-review.googlesource.com/209228
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
4 files changed