Revert of [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 9907415dca8327bf2130fc56a89df3c6c9b792e8..710488a1c300e135cdef661a6ce0949bac8d4928 100644
--- a/src/tracing/tracing-category-observer.cc
+++ b/src/tracing/tracing-category-observer.cc
@@ -18,7 +18,6 @@
   v8::internal::V8::GetCurrentPlatform()->AddTraceStateObserver(
       TracingCategoryObserver::instance_);
   TRACE_EVENT_WARMUP_CATEGORY(TRACE_DISABLED_BY_DEFAULT("v8.runtime_stats"));
-  TRACE_EVENT_WARMUP_CATEGORY(TRACE_DISABLED_BY_DEFAULT("v8.gc_stats"));
 }
 
 void TracingCategoryObserver::TearDown() {
@@ -34,16 +33,10 @@
   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 TracingCategoryObserver::OnTraceDisabled() {
   v8::internal::FLAG_runtime_stats &= ~ENABLED_BY_TRACING;
-  v8::internal::FLAG_gc_stats &= ~ENABLED_BY_TRACING;
 }
 
 }  // namespace tracing