This is a quirk needed for the regexp fuzzer, which passes its own
custom RegExpMatchInfo object to RegExpImpl::Exec and expects execution
without side effects.

Bug: chromium:934621
Change-Id: I90286fda06593d7c574d8d4629481ebad2fa5b1d
Reviewed-on: https://chromium-review.googlesource.com/c/1485833Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59839}