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This CL sets up mac-chrome official try bot, and one of the use cases
is for PGO auto roller to validate the profiles and warm up GOMA
caches for other official builders.

Bug: 1071576
Change-Id: If5ddd46caeccbb5f793b1768ac9790c117055a0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2159766
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#761172}