[Tracing] Use TracingCategoryObserver in gc statistics

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 73018849794af8625fa62bee08179af46712f5f6..a524af14883071213d8c645d6d7da8b31dc453e4 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -5470,7 +5470,7 @@ bool Heap::SetUp() {
   mark_compact_collector_ = new MarkCompactCollector(this);
   gc_idle_time_handler_ = new GCIdleTimeHandler();
   memory_reducer_ = new MemoryReducer(this);
-  if (FLAG_track_gc_object_stats) {
+  if (V8_UNLIKELY(FLAG_gc_stats)) {
     live_object_stats_ = new ObjectStats(this);
     dead_object_stats_ = new ObjectStats(this);
   }