Revert of [Tracing] Use TracingCategoryObserver in runtime statistics

src/tracing/trace-event.cc

Index: src/tracing/trace-event.cc
diff --git a/src/tracing/trace-event.cc b/src/tracing/trace-event.cc
index dd7ce71a6dfb728e6addd951efa8ce2d18538ac5..ebee5345997756c3a77fc902eac3089de7b16369 100644
--- a/src/tracing/trace-event.cc
+++ b/src/tracing/trace-event.cc
@@ -14,6 +14,10 @@
 namespace v8 {
 namespace internal {
 namespace tracing {
+
+// A global flag used as a shortcut to check for the
+// v8.runtime-call-stats category due to its high frequency use.
+base::Atomic32 kRuntimeCallStatsTracingEnabled = false;
 
 v8::Platform* TraceEventHelper::GetCurrentPlatform() {
   return v8::internal::V8::GetCurrentPlatform();