[Tracing] Use TracingCategoryObserver in gc statistics

src/heap/heap-inl.h

Index: src/heap/heap-inl.h
diff --git a/src/heap/heap-inl.h b/src/heap/heap-inl.h
index fc487d0cb70444f0de247121382644841a132828..4932b4483b2226cbd4ad77a7e19308b8b2e9dbb6 100644
--- a/src/heap/heap-inl.h
+++ b/src/heap/heap-inl.h
@@ -12,6 +12,7 @@
 #include "src/heap/heap.h"
 #include "src/heap/incremental-marking-inl.h"
 #include "src/heap/mark-compact.h"
+#include "src/heap/object-stats.h"
 #include "src/heap/remembered-set.h"
 #include "src/heap/spaces-inl.h"
 #include "src/heap/store-buffer.h"
@@ -809,6 +810,16 @@ void Heap::SetSerializedTemplates(FixedArray* templates) {
   set_serialized_templates(templates);
 }
 
+void Heap::CreateObjectStats() {
+  if (V8_LIKELY(FLAG_gc_stats == 0)) return;
+  if (!live_object_stats_) {
+    live_object_stats_ = new ObjectStats(this);
+  }
+  if (!dead_object_stats_) {
+    dead_object_stats_ = new ObjectStats(this);
+  }
+}
+
 AlwaysAllocateScope::AlwaysAllocateScope(Isolate* isolate)
     : heap_(isolate->heap()) {
   heap_->always_allocate_scope_count_.Increment(1);