[heap] Stop concurrent marking tasks in Heap::StartTearDown

Concurrent marking jobs were only joined in Heap::TearDown and
therefore may still update counters while DumpAndResetStats() emits
stats.

This CL stops concurrent marking tasks in Heap::StartTearDown when
also stopping other concurrent tasks like sweeping or unmapping of
pages.

Bug: v8:13175, v8:12775
Change-Id: Iccddbfce5e30002e0db63ba0bdea5ea6b2d5cc40
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3827869Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82849}

src/execution/isolate.cc

@@ -3592,7 +3592,6 @@ void Isolate::Deinit() {
   // not cause a GC.
   heap_.StartTearDown();
 
-  // This stops cancelable tasks (i.e. concurrent marking tasks).
   // Stop concurrent tasks before destroying resources since they might still
   // use those.
   {

src/heap/heap.cc

@@ -5690,6 +5690,10 @@ void Heap::StartTearDown() {
 
   memory_allocator()->unmapper()->EnsureUnmappingCompleted();
 
+  if (FLAG_concurrent_marking) {
+    concurrent_marking()->Pause();
+  }
+
   SetGCState(TEAR_DOWN);
 
   // Background threads may allocate and block until GC is performed. However
@@ -5730,8 +5734,7 @@ void Heap::TearDown() {
   safepoint()->AssertMainThreadIsOnlyThread();
   DCHECK(main_thread_local_heap()->unprotected_memory_chunks_.empty());
 
-  if (FLAG_concurrent_marking || FLAG_parallel_marking)
-    concurrent_marking_->Pause();
+  DCHECK(concurrent_marking()->IsStopped());
 
   // It's too late for Heap::Verify() here, as parts of the Isolate are
   // already gone by the time this is called.