- Eliminates non-const reference parameters in test/cctest.

Bug: v8:9429
Change-Id: I9b3f06d6dda447285673269819bdb405ebac2187
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1793064Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63636}