[profiler] Tracing-based CPU profiler.

src/profiler/tracing-cpu-profiler.h

 // 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.
 
 #ifndef V8_PROFILER_TRACING_CPU_PROFILER_H
 #define V8_PROFILER_TRACING_CPU_PROFILER_H
 
+#include "include/v8-platform.h"
 #include "include/v8-profiler.h"
+#include "src/base/atomic-utils.h"
 #include "src/base/macros.h"
+#include "src/base/platform/mutex.h"
 
 namespace v8 {
 namespace internal {
 
-class TracingCpuProfilerImpl final : public TracingCpuProfiler {
+class CpuProfiler;
+class Isolate;
+
+class TracingCpuProfilerImpl final : public TracingCpuProfiler,
+                                     private v8::Platform::TraceStateObserver {
  public:
   explicit TracingCpuProfilerImpl(Isolate*);
   ~TracingCpuProfilerImpl();
 
+  // v8::Platform::TraceStateObserver
+  void OnTraceEnabled() final;
+  void OnTraceDisabled() final;
+
  private:
+  void StartProfiling();
+  void StopProfiling();
+
+  Isolate* isolate_;
+  std::unique_ptr<CpuProfiler> profiler_;
+  bool profiling_enabled_;
+  base::Mutex mutex_;
+
   DISALLOW_COPY_AND_ASSIGN(TracingCpuProfilerImpl);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PROFILER_TRACING_CPU_PROFILER_H