Forked from email.

The ChromeOS CQ doesn't test changes to the chromeos-chrome ebuild, because it doesn't build chrome from source. In the last month, two CLs have landed to it that needed to be reverted to fix the chrome-pfq:
BuildPackages failed on https://chromium-review.googlesource.com/474237
VMTest failed on https://chromium-review.googlesource.com/463586

Proposal: create a chrome-ebuild-pre-cq config that locally uprevs chrome, and runs through a build/vmtest on some strategically chosen board. This will build chrome from source, so will be slower than a normal pre-cq job, but use a COMMIT-QUEUE.ini such that it only runs on changes to chromeos-chrome-9999.ebuild.