TSAN was flakily detecting a race in the Add/RemoveSampler functions.
It could also be fixed by moving the USE(atomic_->Value()); line below
the do loop in the constructor of AtomicGuard.

Given that base::AtomicValue is deprecated and std::atomic has a
compare_exchange operation with std::memory_order_seq_cst, we can just
use std::atomic_bool to fix the TSAN false-positive.

Bug: v8:7702
Change-Id: Id2038ea1ccced7339f45991263e944394e935454
Reviewed-on: https://chromium-review.googlesource.com/c/1288814Reviewed-by: Alexei Filippov <alph@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56794}