GitLab

This lays out a skeleton for the document, plus fills in some details of
how to go from a build results page to the test that flaked.

Bug: 1127369
Change-Id: Icea0ef102d694a61cf8f390c563ce108afee0553
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2405418
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815262}