[code coverage] Spin up builder for custom oobe reports.

This builder is expected to run code coverage builds with custom
modifications for the code mauve effort.

R=stgao,liaoyuke,jbudorick

NOTRY=true

Bug: 953123
Change-Id: I324de432632401db5956944225380144e7b23e3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1572926
Commit-Queue: Roberto Carrillo <robertocn@chromium.org>
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652972}
7 files changed