The tests were not flushing the i-cache before calling the generated
code. Use Factory::NewCode to make sure that the i-cache is flushed
instead.

Bug: v8:7977
Change-Id: I9c7c6f0d0e31700634e50279e75858a5d74603d8
Reviewed-on: https://chromium-review.googlesource.com/1150165Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Cr-Commit-Position: refs/heads/master@{#54711}