[Tracing] Use TracingCategoryObserver in runtime statistics

src/compiler-dispatcher/compiler-dispatcher-tracer.cc

Index: src/compiler-dispatcher/compiler-dispatcher-tracer.cc
diff --git a/src/compiler-dispatcher/compiler-dispatcher-tracer.cc b/src/compiler-dispatcher/compiler-dispatcher-tracer.cc
index 81029c71b4581c528e158dd05a87f1fbce85ef73..434d7b5bd0fb6e7a1ccc7a9f421b35a20d8ff2a8 100644
--- a/src/compiler-dispatcher/compiler-dispatcher-tracer.cc
+++ b/src/compiler-dispatcher/compiler-dispatcher-tracer.cc
@@ -23,8 +23,7 @@ CompilerDispatcherTracer::Scope::Scope(CompilerDispatcherTracer* tracer,
     : tracer_(tracer), scope_id_(scope_id), num_(num) {
   start_time_ = MonotonicallyIncreasingTimeInMs();
   // TODO(cbruni): remove once we fully moved to a trace-based system.
-  if (TRACE_EVENT_RUNTIME_CALL_STATS_TRACING_ENABLED() ||
-      FLAG_runtime_call_stats) {
+  if (FLAG_runtime_stats) {

[Camillo Bruni, 2016/10/31 09:59:49]

nit: I think you want to use the V8_UNLIKELY(FLAG_runtime_stats) almost
everywhere.

[lpy, 2016/10/31 17:28:02]

Done.

     RuntimeCallStats::Enter(tracer_->runtime_call_stats_, &timer_,
                             &RuntimeCallStats::CompilerDispatcher);
   }
@@ -53,8 +52,7 @@ CompilerDispatcherTracer::Scope::~Scope() {
       break;
   }
   // TODO(cbruni): remove once we fully moved to a trace-based system.
-  if (TRACE_EVENT_RUNTIME_CALL_STATS_TRACING_ENABLED() ||
-      FLAG_runtime_call_stats) {
+  if (FLAG_runtime_stats) {
     RuntimeCallStats::Leave(tracer_->runtime_call_stats_, &timer_);
   }
 }