This will allow us to use ScopedPtrList for other contents than just
pointers.

Change-Id: Ib16d388d5dd556f5e01593279f463ae25510f2be
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1715455Reviewed-by: Dan Elphick <delphick@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62898}