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This allows us to run CELab tests on Chrome.
"Choose tryjobs" now has two flavors of celab bots (chromium & chrome).

Chrome tests are needed for certain scenarios,
e.g. CloudManagementEnrollmentTokenTest: https://crrev.com/c/1779440

Config based on our existing Chromium bots, but added
'official' to get official chrome-branded builds:
  https://crrev.com/c/1841581

Which now works with the new bot & config:
  https://crrev.com/c/1836153

Based on https://crrev.com/i/1930512.

Bug: 1004563
Change-Id: Ia00cef7be4b0a6164e15b250052d867376edc139
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1836602Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Mathieu Binette <mbinette@google.com>
Cr-Commit-Position: refs/heads/master@{#703887}