[Tracing] Use TracingCategoryObserver in gc statistics

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index 3a88eebdccb79d1f98b3c1e32c24a01aaf693ab0..ce7d8782a8601c1a9f8be61b04f51631f173f8f2 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -25,6 +25,7 @@
 #include "src/heap/spaces-inl.h"
 #include "src/ic/ic.h"
 #include "src/ic/stub-cache.h"
+#include "src/tracing/tracing-category-observer.h"
 #include "src/utils-inl.h"
 #include "src/v8.h"
 
@@ -2236,17 +2237,21 @@ void MarkCompactCollector::VisitAllObjects(HeapObjectVisitor* visitor) {
 }
 
 void MarkCompactCollector::RecordObjectStats() {
-  if (FLAG_track_gc_object_stats) {
+  if (V8_UNLIKELY(FLAG_gc_stats)) {
+    heap()->CreateObjectStats();
     ObjectStatsVisitor visitor(heap(), heap()->live_object_stats_,
                                heap()->dead_object_stats_);
     VisitAllObjects(&visitor);
-    std::stringstream live, dead;
-    heap()->live_object_stats_->Dump(live);
-    heap()->dead_object_stats_->Dump(dead);
-    TRACE_EVENT_INSTANT2(TRACE_DISABLED_BY_DEFAULT("v8.gc_stats"),
-                         "V8.GC_Objects_Stats", TRACE_EVENT_SCOPE_THREAD,
-                         "live", TRACE_STR_COPY(live.str().c_str()), "dead",
-                         TRACE_STR_COPY(dead.str().c_str()));
+    if (V8_UNLIKELY(FLAG_gc_stats &
+                    v8::tracing::TracingCategoryObserver::ENABLED_BY_TRACING)) {
+      std::stringstream live, dead;
+      heap()->live_object_stats_->Dump(live);
+      heap()->dead_object_stats_->Dump(dead);
+      TRACE_EVENT_INSTANT2(TRACE_DISABLED_BY_DEFAULT("v8.gc_stats"),
+                           "V8.GC_Objects_Stats", TRACE_EVENT_SCOPE_THREAD,
+                           "live", TRACE_STR_COPY(live.str().c_str()), "dead",
+                           TRACE_STR_COPY(dead.str().c_str()));
+    }
     if (FLAG_trace_gc_object_stats) {
       heap()->live_object_stats_->PrintJSON("live");
       heap()->dead_object_stats_->PrintJSON("dead");