For the first test, we just test that we can search on two threads at
the same time. This CL sets the base for the future tests for more
complicated cases.

Bug: v8:7790
Change-Id: I1becf4493897b55e7ee0a7f37ab5bf1203bf14eb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2241530
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68838}