[Tracing] Create TracingCategoryObserver in gin/.

gin/v8_platform.cc

 // Copyright 2014 The Chromium 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 "gin/public/v8_platform.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/sys_info.h"
 #include "base/threading/worker_pool.h"
 #include "base/trace_event/trace_event.h"
 #include "gin/per_isolate_data.h"
+#include "v8/include/v8-tracing.h"
 
 namespace gin {
 
 namespace {
 
 base::LazyInstance<V8Platform>::Leaky g_v8_platform = LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
 // static
@@ skipping 124 matching lines @@
   memcpy(&traceEventHandle, &handle, sizeof(handle));
   TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(category_enabled_flag, name,
                                               traceEventHandle);
 }
 
 namespace {
 
 class EnabledStateObserverImpl final
     : public base::trace_event::TraceLog::EnabledStateObserver {
  public:
-  EnabledStateObserverImpl() = default;
+  EnabledStateObserverImpl() {
+    tracing_category_observer_ = v8::tracing::TracingCategoryObserver::Create();

[alph, 2016/10/31 22:48:55]

Why it belongs here? It should be an internal class in V8.

+    observers_.insert(reinterpret_cast<v8::Platform::TraceStateObserver*>(

[alph, 2016/10/31 22:48:55]

Reinterpret cast between interfaces won't work.

+        tracing_category_observer_.get()));
+  }
 
   void OnTraceLogEnabled() final {
     base::AutoLock lock(mutex_);
     for (auto o : observers_) {
       o->OnTraceEnabled();
     }
   }
 
   void OnTraceLogDisabled() final {
     base::AutoLock lock(mutex_);
@@ skipping 17 matching lines @@
     observers_.erase(observer);
     if (observers_.empty()) {
       base::trace_event::TraceLog::GetInstance()->RemoveEnabledStateObserver(
           this);
     }
   }
 
  private:
   base::Lock mutex_;
   std::unordered_set<v8::Platform::TraceStateObserver*> observers_;
+  std::unique_ptr<v8::tracing::TracingCategoryObserver>
+      tracing_category_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(EnabledStateObserverImpl);
 };
 
 base::LazyInstance<EnabledStateObserverImpl>::Leaky g_trace_state_dispatcher =
     LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
 void V8Platform::AddTraceStateObserver(
     v8::Platform::TraceStateObserver* observer) {
   g_trace_state_dispatcher.Get().AddObserver(observer);
 }
 
 void V8Platform::RemoveTraceStateObserver(
     v8::Platform::TraceStateObserver* observer) {
   g_trace_state_dispatcher.Get().RemoveObserver(observer);
 }
 
 }  // namespace gin