[runtimecallstats] Fix data race in WorkerThreadRuntimeCallStats

Change-Id: I8fff5e5b3d61f1054efdb4fc7f8fa2b50180e418
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2523195Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71011}

src/logging/counters.cc

@@ -609,6 +609,7 @@ WorkerThreadRuntimeCallStats::~WorkerThreadRuntimeCallStats() {
 }
 
 base::Thread::LocalStorageKey WorkerThreadRuntimeCallStats::GetKey() {
+  base::MutexGuard lock(&mutex_);
   DCHECK(TracingFlags::is_runtime_stats_enabled());
   if (!tls_key_) tls_key_ = base::Thread::CreateThreadLocalKey();
   return *tls_key_;