GitLab

* Say more about the relationship to virtual/stable

* Say more about the different contexts tested, and call out the
  service worker and worklet tests that live elsewhere in the tree.

* Say more about the platform specific listings and there those
  results live.

* Call out caveat about inheritance changes.

Change-Id: Ifc750986f2b560ecc6c819bffd501b868a8d9da5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2278605
Commit-Queue: Joshua Bell <jsbell@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Jarryd Goodman <jarrydg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#787872}