Errors during the download should be reported as such, not as "failed to grab
the lock file".

R=nodir@chromium.org, iannucci@chromium.org
BUG=853722

Change-Id: If24f4587693852eed0608450bcd311cf3bafd2c3
Reviewed-on: https://chromium-review.googlesource.com/1226106Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>