[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 f9315b4ce456beb5d55b0b02c6ca06d00e6b006e..818cad1438d93cf61b5a34acc34663385a12ac00 100644
--- a/src/tracing/tracing-category-observer.cc
+++ b/src/tracing/tracing-category-observer.cc
@@ -17,7 +17,9 @@ std::unique_ptr<TracingCategoryObserver> TracingCategoryObserver::Create() {
       new TracingCategoryObserverImpl());
 }
 
-TracingCategoryObserverImpl::TracingCategoryObserverImpl() {}
+TracingCategoryObserverImpl::TracingCategoryObserverImpl() {
+  TRACE_EVENT_WARMUP_CATEGORY(TRACE_DISABLED_BY_DEFAULT("v8.gc_stats"));
+}
 
 TracingCategoryObserverImpl::~TracingCategoryObserverImpl() {
   OnTraceDisabled();
@@ -30,10 +32,16 @@ void TracingCategoryObserverImpl::OnTraceEnabled() {
   if (enabled) {
     v8::internal::FLAG_runtime_stats |= ENABLED_BY_TRACING;
   }
+  TRACE_EVENT_CATEGORY_GROUP_ENABLED(TRACE_DISABLED_BY_DEFAULT("v8.gc_stats"),
+                                     &enabled);
+  if (enabled) {
+    v8::internal::FLAG_gc_stats |= ENABLED_BY_TRACING;
+  }
 }
 
 void TracingCategoryObserverImpl::OnTraceDisabled() {
   v8::internal::FLAG_runtime_stats &= ~ENABLED_BY_TRACING;
+  v8::internal::FLAG_gc_stats &= ~ENABLED_BY_TRACING;
 }
 
 }  // namespace tracing