The {CommentOperator}, used for implementing the --code-comments flag,
is not UBSan-safe. This CL fixes this and adds a test which uses code
comments.

R=bmeurer@chromium.org

Bug: v8:7744
Change-Id: Ia6ec509e77d998df085ac7377cb24854354e3aa2
Reviewed-on: https://chromium-review.googlesource.com/1051235
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53100}