This is a reland of 8aa6b15f with a fix
for TSAN failures.

Original change's description:
> Disable bytecode flushing once we toggle coverage mode.
>
> Changing coverage mode generated different bytecode in some cases.
> Hence it is not safe to flush bytecode once we toggle coverage mode.
>
> Bug: chromium:1147917
> Change-Id: I9e640aeaec664d3d4a4aaedf809c568e9ad924fc
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2615020
> Commit-Queue: Mythri Alle <mythria@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#71985}

Bug: chromium:1147917
Change-Id: Ibd8c4feb8615ba7b92fe547c55d455958c94c526
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2624612
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72062}