Port 19953355

Original Commit Message:

    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=clemensh@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: Ia7976ec9a726fdeb7d8bfbb99c8a16d473aa0da4
Reviewed-on: https://chromium-review.googlesource.com/1157230Reviewed-by: Muntasir Mallick <mmallick@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#54828}