[tracing] Implement Add/RemoveTraceStateObserver for default platform.

src/libplatform/default-platform.h

 // Copyright 2013 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.
 
 #ifndef V8_LIBPLATFORM_DEFAULT_PLATFORM_H_
 #define V8_LIBPLATFORM_DEFAULT_PLATFORM_H_
 
 #include <functional>
 #include <map>
 #include <queue>
@@ skipping 43 matching lines @@
   uint64_t AddTraceEvent(char phase, const uint8_t* category_enabled_flag,
                          const char* name, const char* scope, uint64_t id,
                          uint64_t bind_id, int32_t num_args,
                          const char** arg_names, const uint8_t* arg_types,
                          const uint64_t* arg_values,
                          unsigned int flags) override;
   void UpdateTraceEventDuration(const uint8_t* category_enabled_flag,
                                 const char* name, uint64_t handle) override;
   void SetTracingController(tracing::TracingController* tracing_controller);
 
+  void AddTraceStateObserver(TraceStateObserver* observer) override;
+  void RemoveTraceStateObserver(TraceStateObserver* observer) override;
+
  private:
   static const int kMaxThreadPoolSize;
 
   Task* PopTaskInMainThreadQueue(v8::Isolate* isolate);
   Task* PopTaskInMainThreadDelayedQueue(v8::Isolate* isolate);
 
   base::Mutex lock_;
   bool initialized_;
   int thread_pool_size_;
   std::vector<WorkerThread*> thread_pool_;
   TaskQueue queue_;
   std::map<v8::Isolate*, std::queue<Task*> > main_thread_queue_;
 
   typedef std::pair<double, Task*> DelayedEntry;
   std::map<v8::Isolate*,
            std::priority_queue<DelayedEntry, std::vector<DelayedEntry>,
                                std::greater<DelayedEntry> > >
       main_thread_delayed_queue_;
   tracing::TracingController* tracing_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(DefaultPlatform);
 };
 
 
 }  // namespace platform
 }  // namespace v8
 
 
 #endif  // V8_LIBPLATFORM_DEFAULT_PLATFORM_H_