When adding the new heuristic to allocate registers that do not
take part in hinting first, I managed to break hinting for most
cases. This change makes hinting operational again.

Bug: chromium:920106
Change-Id: I0f460a66196087266dcb70a7a0e5569124bdd2ff
Reviewed-on: https://chromium-review.googlesource.com/c/1402791Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Stephan Herhut <herhut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58669}