[Tracing] Implement TracingCategoryObserver.

src/d8.cc

 // Copyright 2012 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 <errno.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 
 #include <algorithm>
@@ skipping 130 matching lines @@
   }
 
  private:
   double synthetic_time_in_sec_ = 0.0;
 
   DISALLOW_COPY_AND_ASSIGN(PredictablePlatform);
 };
 
 
 v8::Platform* g_platform = NULL;
+std::unique_ptr<Platform::TracingFlag> g_tracing_flag;
 
 
 static Local<Value> Throw(Isolate* isolate, const char* message) {
   return isolate->ThrowException(
       String::NewFromUtf8(isolate, message, NewStringType::kNormal)
           .ToLocalChecked());
 }
 
 
 bool FindInObjectList(Local<Object> object, const Shell::ObjectList& list) {
@@ skipping 2575 matching lines @@
         int size = 0;
         char* trace_config_json_str =
             ReadChars(nullptr, options.trace_config, &size);
         trace_config =
             tracing::CreateTraceConfigFromJSON(isolate, trace_config_json_str);
         delete[] trace_config_json_str;
       } else {
         trace_config =
             platform::tracing::TraceConfig::CreateDefaultTraceConfig();
       }
-      tracing_controller->Initialize(trace_buffer);
-      tracing_controller->StartTracing(trace_config);
       if (!i::FLAG_verify_predictable) {
         platform::SetTracingController(g_platform, tracing_controller);
       }
+      tracing_controller->Initialize(trace_buffer);
+      g_tracing_flag = Platform::TracingFlag::Create();
+      tracing_controller->StartTracing(trace_config);
     }
 
     if (options.dump_heap_constants) {
       DumpHeapConstants(reinterpret_cast<i::Isolate*>(isolate));
       return 0;
     }
 
     if (options.stress_opt || options.stress_deopt) {
       Testing::SetStressRunType(options.stress_opt
                                 ? Testing::kStressTypeOpt
@@ skipping 53 matching lines @@
 }
 
 }  // namespace v8
 
 
 #ifndef GOOGLE3
 int main(int argc, char* argv[]) {
   return v8::Shell::Main(argc, argv);
 }
 #endif