We only use IsParked from the thread that owns the LocalHeap, which is
the only thread which mutates state_. So it is safe to read state_ from
that thread without a mutex.

Bug: v8:10315
Change-Id: I3725ca4c4c4da1c661d7b4f06d295312914b4b52
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2332168Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69172}