Concurrent allocation uses Isolate::is_profiling() to determine
whether logging is on. This races with the main thread when the
value in is_profiling is switched on/off by the cpu profiler.

Fix this by making is_profiling relaxed atomic. The profiler doesn't
turn off logging for correctness reasons, so it is fine when background
threads may read an old value and continue logging a bit longer. It is
also okay when background threads start logging again a bit longer when
profiling is stopped.

Bug: v8:10315
Change-Id: Id52d06f7a8239e10dfa63da38e761b2c00a2da4b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2404779
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69882}