You say you have to rely on humans and heuristics to determine which CL to revert. Couldn't you automatically re-run just the failing tests on the batch?

More importantly, you seem to be running all the tests, as often as you can. A commit changing a text label shouldn't require running all the tests, that just doesn't scale. Have you consider splitting Chromium into different projects, where commits for one project would result in the tests of that project, and only that project?