This reduces the enum size to only take up one byte, hence decreasing
class size.

Bug: v8:7926
Change-Id: Ie50cfcd48541e44394814f375fd72f2b65722fdf
Reviewed-on: https://chromium-review.googlesource.com/1186582
Commit-Queue: Florian Sattler <sattlerf@google.com>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55378}