This is mainly to enable optimization of case-insensitive maps, where
we see the pattern

if (m.has(key.toLowerCase())) { return m.get(key.toLowerCase()) } ...

Cq-Include-Trybots: master.tryserver.v8:v8_linux_noi18n_rel_ng
Change-Id: I8c78a185401c51e8a53ae2932a158eaafa169495
Reviewed-on: https://chromium-review.googlesource.com/547057
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46206}