Fixed problem with to_string

Bug: v8:9855
Change-Id: I5fdd9e77e78a77ab5a9aad833d8ac71bebd1a291
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1886910Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Liviu Rau <liviurau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64613}