Apart from being more in-line with the style guide, this allows to use
DEFINE_LAZY_LEAKY_OBJECT_GETTER for defining {TypeCache::Get}.

R=tebbi@chromium.org

Bug: v8:8562
Change-Id: I016b28624950ce9404180fc1ca1a232551f75cd0
Reviewed-on: https://chromium-review.googlesource.com/c/1392201Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58500}