Preparation for sharing more code between deopt fuzzer and normal test runner.

Bug: v8:6917
Change-Id: Id8022c7597544ffddf5d1b0a0d73bb4a9d163fc3
Reviewed-on: https://chromium-review.googlesource.com/715417
Commit-Queue: Michał Majewski <majeski@google.com>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48521}