[Tracing] Use TracingCategoryObserver in gc statistics

src/tracing/tracing-category-observer.cc

Index: src/tracing/tracing-category-observer.cc
diff --git a/src/tracing/tracing-category-observer.cc b/src/tracing/tracing-category-observer.cc
index e6bd06ae17547fa2257152c1fb23eee2d20111c6..3fffd2f9ca63d23b396752c71b754525be66337e 100644
--- a/src/tracing/tracing-category-observer.cc
+++ b/src/tracing/tracing-category-observer.cc
@@ -20,6 +20,7 @@ void TracingCategoryObserver::SetUp() {
   TRACE_EVENT_WARMUP_CATEGORY(TRACE_DISABLED_BY_DEFAULT("v8.runtime_stats"));
   TRACE_EVENT_WARMUP_CATEGORY(
       TRACE_DISABLED_BY_DEFAULT("v8.runtime_stats_sampling"));
+  TRACE_EVENT_WARMUP_CATEGORY(TRACE_DISABLED_BY_DEFAULT("v8.gc_stats"));
 }
 
 void TracingCategoryObserver::TearDown() {
@@ -40,11 +41,17 @@ void TracingCategoryObserver::OnTraceEnabled() {
   if (enabled) {
     v8::internal::FLAG_runtime_stats |= ENABLED_BY_SAMPLING;
   }
+  TRACE_EVENT_CATEGORY_GROUP_ENABLED(TRACE_DISABLED_BY_DEFAULT("v8.gc_stats"),
+                                     &enabled);
+  if (enabled) {
+    v8::internal::FLAG_gc_stats |= ENABLED_BY_TRACING;
+  }
 }
 
 void TracingCategoryObserver::OnTraceDisabled() {
   v8::internal::FLAG_runtime_stats &=
       ~(ENABLED_BY_TRACING | ENABLED_BY_SAMPLING);
+  v8::internal::FLAG_gc_stats &= ~ENABLED_BY_TRACING;
 }
 
 }  // namespace tracing