[Tracing] Make TracingCategoryObserver v8 internal.

src/tracing/tracing-category-observer.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/tracing/tracing-category-observer.h"
 
 #include "include/v8.h"
 #include "src/flags.h"
 #include "src/tracing/trace-event.h"
 #include "src/v8.h"
 
 namespace v8 {
 namespace tracing {
 
-std::unique_ptr<TracingCategoryObserver> TracingCategoryObserver::Create() {
-  return std::unique_ptr<TracingCategoryObserver>(
-      new TracingCategoryObserverImpl());
+std::unique_ptr<TracingCategoryObserver> g_tracing_category_observer;

[alph, 2016/11/02 20:18:23]

nit: You can make it a static field inside the class.

[lpy, 2016/11/02 21:52:27]

Done.

+
+void TracingCategoryObserver::SetUp() {
+  g_tracing_category_observer.reset(new TracingCategoryObserver());
+  v8::internal::V8::GetCurrentPlatform()->AddTraceStateObserver(
+      g_tracing_category_observer.get());
 }
 
-TracingCategoryObserverImpl::TracingCategoryObserverImpl() {}
-
-TracingCategoryObserverImpl::~TracingCategoryObserverImpl() {
-  OnTraceDisabled();
+void TracingCategoryObserver::TearDown() {
+  v8::internal::V8::GetCurrentPlatform()->RemoveTraceStateObserver(
+      g_tracing_category_observer.get());
+  g_tracing_category_observer.reset();
 }
 
-void TracingCategoryObserverImpl::OnTraceEnabled() {
+void TracingCategoryObserver::OnTraceEnabled() {
   bool enabled = false;
   TRACE_EVENT_CATEGORY_GROUP_ENABLED(
       TRACE_DISABLED_BY_DEFAULT("v8.runtime_stats"), &enabled);
   if (enabled) {
     v8::internal::FLAG_runtime_stats |= ENABLED_BY_TRACING;
   }
 }
 
-void TracingCategoryObserverImpl::OnTraceDisabled() {
+void TracingCategoryObserver::OnTraceDisabled() {
   v8::internal::FLAG_runtime_stats &= ~ENABLED_BY_TRACING;
 }
 
 }  // namespace tracing
 }  // namespace v8