[Tracing] Use TracingCategoryObserver in runtime 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..dcf67253071351d51e9aa28d7c4cee87b7b96727 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.runtime_stats"));
+}
 
 TracingCategoryObserverImpl::~TracingCategoryObserverImpl() {
   OnTraceDisabled();
@@ -33,7 +35,7 @@ void TracingCategoryObserverImpl::OnTraceEnabled() {
 }
 
 void TracingCategoryObserverImpl::OnTraceDisabled() {
-  v8::internal::FLAG_runtime_stats &= ~ENABLED_BY_TRACING;
+  v8::internal::FLAG_runtime_stats ^= ENABLED_BY_TRACING;

[alph, 2016/10/31 20:46:53]

This won't work. The category might not have been enabled before.

[lpy, 2016/10/31 20:54:19]

Done.

ah you are right, I think the original one will work.

 }
 
 }  // namespace tracing