cppgc: Extract not fully constructed objects atomically

Parallel marking is running at the beginning of the atomic pause, so the
extraction of these objects must happen atomically.

Bug: v8:13045
Change-Id: I90d489597847e76ade7185cd7120816eddcdc9fe
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3749204Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81593}

src/heap/cppgc/marker.cc

@@ -676,8 +676,11 @@ void MarkerBase::MarkNotFullyConstructedObjects() {
   StatsCollector::DisabledScope stats_scope(
       heap().stats_collector(),
       StatsCollector::kMarkVisitNotFullyConstructedObjects);
+  // Parallel marking may still be running which is why atomic extraction is
+  // required.
   std::unordered_set<HeapObjectHeader*> objects =
-      mutator_marking_state_.not_fully_constructed_worklist().Extract();
+      mutator_marking_state_.not_fully_constructed_worklist()
+          .Extract<AccessMode::kAtomic>();
   for (HeapObjectHeader* object : objects) {
     DCHECK(object);
     // TraceConservativelyIfNeeded delegates to either in-construction or