This type is dangerous because it can become smaller over time (as
strings get internalized).

Bug: v8:6521
Change-Id: Iea650789ab52c13a0519f46999edc8a7959ccc71
Reviewed-on: https://chromium-review.googlesource.com/968525
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52040}