Reland [Tracing] V8 Tracing Controller

V8 has had a trace event macro interface for while, but without a tracing
controller a standalone V8 would be unable to collect traces.

This CL introduces a complete Tracing Controller system for V8.
It is fully function except that it does not yet store trace event args.

This CL has a few components,
The tracing controller itself, contributed by the author of this CL
The Trace config (including the parser), contributed by lpy@
The Trace Object, Trace Writer, and Trace Buffer are all contributed by rksang@

BUG=v8:4561
LOG=N

The original CL was failing the V8 Arm Builder:
https://build.chromium.org/p/client.v8.ports/builders/V8%20Arm%20-%20builder/builds/2456
and the V8 Mips Builder:
https://build.chromium.org/p/client.v8.ports/builders/V8%20Mips%20-%20builder/builds/2506

The failure is due to undefined behavior of CHECK_EQ of 2 const char*

Fix in patch #1

Committed: https://crrev.com/3d598452679ce208ad9b2f48e0fb3fae352ce375
Cr-Commit-Position: refs/heads/master@{#38073}

patch from issue 2137013006 at patchset 200001 (http://crrev.com/2137013006#ps200001)

Review-Url: https://codereview.chromium.org/2183923004
Cr-Commit-Position: refs/heads/master@{#38104}

BUILD.gn

@@ -2114,10 +2114,18 @@ v8_source_set("v8_libbase") {
 v8_source_set("v8_libplatform") {
   sources = [
     "include/libplatform/libplatform.h",
+    "include/libplatform/v8-tracing.h",
     "src/libplatform/default-platform.cc",
     "src/libplatform/default-platform.h",
     "src/libplatform/task-queue.cc",
     "src/libplatform/task-queue.h",
+    "src/libplatform/tracing/trace-buffer.cc",
+    "src/libplatform/tracing/trace-buffer.h",
+    "src/libplatform/tracing/trace-config.cc",
+    "src/libplatform/tracing/trace-object.cc",
+    "src/libplatform/tracing/trace-writer.cc",
+    "src/libplatform/tracing/trace-writer.h",
+    "src/libplatform/tracing/tracing-controller.cc",
     "src/libplatform/worker-thread.cc",
     "src/libplatform/worker-thread.h",
   ]

include/libplatform/libplatform.h

@@ -5,6 +5,7 @@
 #ifndef V8_LIBPLATFORM_LIBPLATFORM_H_
 #define V8_LIBPLATFORM_LIBPLATFORM_H_
 
+#include "include/libplatform/v8-tracing.h"
 #include "v8-platform.h"  // NOLINT(build/include)
 
 namespace v8 {
@@ -31,6 +32,14 @@ v8::Platform* CreateDefaultPlatform(int thread_pool_size = 0);
  */
 bool PumpMessageLoop(v8::Platform* platform, v8::Isolate* isolate);
 
+/**
+ * Attempts to set the tracing controller for the given platform.
+ *
+ * The |platform| has to be created using |CreateDefaultPlatform|.
+ */
+void SetTracingController(
+    v8::Platform* platform,
+    v8::platform::tracing::TracingController* tracing_controller);
 
 }  // namespace platform
 }  // namespace v8

include/libplatform/v8-tracing.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_LIBPLATFORM_V8_TRACING_H_
+#define V8_LIBPLATFORM_V8_TRACING_H_
+
+#include <fstream>
+#include <memory>
+#include <vector>
+
+namespace v8 {
+namespace platform {
+namespace tracing {
+
+class TraceObject {
+ public:
+  TraceObject() {}
+  void Initialize(char phase, const uint8_t* category_enabled_flag,
+                  const char* name, const char* scope, uint64_t id,
+                  uint64_t bind_id, int num_args, const char** arg_names,
+                  const uint8_t* arg_types, const uint64_t* arg_values,
+                  unsigned int flags);
+  void UpdateDuration();
+  void InitializeForTesting(char phase, const uint8_t* category_enabled_flag,
+                            const char* name, const char* scope, uint64_t id,
+                            uint64_t bind_id, int num_args,
+                            const char** arg_names, const uint8_t* arg_types,
+                            const uint64_t* arg_values, unsigned int flags,
+                            int pid, int tid, int64_t ts, int64_t tts,
+                            uint64_t duration, uint64_t cpu_duration);
+
+  int pid() const { return pid_; }
+  int tid() const { return tid_; }
+  char phase() const { return phase_; }
+  const uint8_t* category_enabled_flag() const {
+    return category_enabled_flag_;
+  }
+  const char* name() const { return name_; }
+  const char* scope() const { return scope_; }
+  uint64_t id() const { return id_; }
+  uint64_t bind_id() const { return bind_id_; }
+  unsigned int flags() const { return flags_; }
+  int64_t ts() { return ts_; }
+  int64_t tts() { return tts_; }
+  uint64_t duration() { return duration_; }
+  uint64_t cpu_duration() { return cpu_duration_; }
+
+ private:
+  int pid_;
+  int tid_;
+  char phase_;
+  const char* name_;
+  const char* scope_;
+  const uint8_t* category_enabled_flag_;
+  uint64_t id_;
+  uint64_t bind_id_;
+  int num_args_;
+  unsigned int flags_;
+  int64_t ts_;
+  int64_t tts_;
+  uint64_t duration_;
+  uint64_t cpu_duration_;
+  // TODO(fmeawad): Add args support.
+
+  // Disallow copy and assign
+  TraceObject(const TraceObject&) = delete;
+  void operator=(const TraceObject&) = delete;
+};
+
+class TraceWriter {
+ public:
+  TraceWriter() {}
+  virtual ~TraceWriter() {}
+  virtual void AppendTraceEvent(TraceObject* trace_event) = 0;
+  virtual void Flush() = 0;
+
+  static TraceWriter* CreateJSONTraceWriter(std::ostream& stream);
+
+ private:
+  // Disallow copy and assign
+  TraceWriter(const TraceWriter&) = delete;
+  void operator=(const TraceWriter&) = delete;
+};
+
+class TraceBufferChunk {
+ public:
+  explicit TraceBufferChunk(uint32_t seq);
+
+  void Reset(uint32_t new_seq);
+  bool IsFull() const { return next_free_ == kChunkSize; }
+  TraceObject* AddTraceEvent(size_t* event_index);
+  TraceObject* GetEventAt(size_t index) { return &chunk_[index]; }
+
+  uint32_t seq() const { return seq_; }
+  size_t size() const { return next_free_; }
+
+  static const size_t kChunkSize = 64;
+
+ private:
+  size_t next_free_ = 0;
+  TraceObject chunk_[kChunkSize];
+  uint32_t seq_;
+
+  // Disallow copy and assign
+  TraceBufferChunk(const TraceBufferChunk&) = delete;
+  void operator=(const TraceBufferChunk&) = delete;
+};
+
+class TraceBuffer {
+ public:
+  TraceBuffer() {}
+  virtual ~TraceBuffer() {}
+
+  virtual TraceObject* AddTraceEvent(uint64_t* handle) = 0;
+  virtual TraceObject* GetEventByHandle(uint64_t handle) = 0;
+  virtual bool Flush() = 0;
+
+  static const size_t kRingBufferChunks = 1024;
+
+  static TraceBuffer* CreateTraceBufferRingBuffer(size_t max_chunks,
+                                                  TraceWriter* trace_writer);
+
+ private:
+  // Disallow copy and assign
+  TraceBuffer(const TraceBuffer&) = delete;
+  void operator=(const TraceBuffer&) = delete;
+};
+
+// Options determines how the trace buffer stores data.
+enum TraceRecordMode {
+  // Record until the trace buffer is full.
+  RECORD_UNTIL_FULL,
+
+  // Record until the user ends the trace. The trace buffer is a fixed size
+  // and we use it as a ring buffer during recording.
+  RECORD_CONTINUOUSLY,
+
+  // Record until the trace buffer is full, but with a huge buffer size.
+  RECORD_AS_MUCH_AS_POSSIBLE,
+
+  // Echo to console. Events are discarded.
+  ECHO_TO_CONSOLE,
+};
+
+class TraceConfig {
+ public:
+  typedef std::vector<std::string> StringList;
+
+  TraceConfig()
+      : enable_sampling_(false),
+        enable_systrace_(false),
+        enable_argument_filter_(false) {}
+  TraceRecordMode GetTraceRecordMode() const { return record_mode_; }
+  bool IsSamplingEnabled() const { return enable_sampling_; }
+  bool IsSystraceEnabled() const { return enable_systrace_; }
+  bool IsArgumentFilterEnabled() const { return enable_argument_filter_; }
+
+  void SetTraceRecordMode(TraceRecordMode mode) { record_mode_ = mode; }
+  void EnableSampling() { enable_sampling_ = true; }
+  void EnableSystrace() { enable_systrace_ = true; }
+  void EnableArgumentFilter() { enable_argument_filter_ = true; }
+
+  void AddIncludedCategory(const char* included_category);
+  void AddExcludedCategory(const char* excluded_category);
+
+  bool IsCategoryGroupEnabled(const char* category_group) const;
+
+ private:
+  TraceRecordMode record_mode_;
+  bool enable_sampling_ : 1;
+  bool enable_systrace_ : 1;
+  bool enable_argument_filter_ : 1;
+  StringList included_categories_;
+  StringList excluded_categories_;
+
+  // Disallow copy and assign
+  TraceConfig(const TraceConfig&) = delete;
+  void operator=(const TraceConfig&) = delete;
+};
+
+class TracingController {
+ public:
+  enum Mode { DISABLED = 0, RECORDING_MODE };
+
+  // The pointer returned from GetCategoryGroupEnabledInternal() points to a
+  // value with zero or more of the following bits. Used in this class only.
+  // The TRACE_EVENT macros should only use the value as a bool.
+  // These values must be in sync with macro values in TraceEvent.h in Blink.
+  enum CategoryGroupEnabledFlags {
+    // Category group enabled for the recording mode.
+    ENABLED_FOR_RECORDING = 1 << 0,
+    // Category group enabled by SetEventCallbackEnabled().
+    ENABLED_FOR_EVENT_CALLBACK = 1 << 2,
+    // Category group enabled to export events to ETW.
+    ENABLED_FOR_ETW_EXPORT = 1 << 3
+  };
+
+  TracingController() {}
+  void Initialize(TraceBuffer* trace_buffer);
+  const uint8_t* GetCategoryGroupEnabled(const char* category_group);
+  static const char* GetCategoryGroupName(const uint8_t* category_enabled_flag);
+  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);
+  void UpdateTraceEventDuration(const uint8_t* category_enabled_flag,
+                                const char* name, uint64_t handle);
+
+  void StartTracing(TraceConfig* trace_config);
+  void StopTracing();
+
+ private:
+  const uint8_t* GetCategoryGroupEnabledInternal(const char* category_group);
+  void UpdateCategoryGroupEnabledFlag(size_t category_index);
+  void UpdateCategoryGroupEnabledFlags();
+
+  std::unique_ptr<TraceBuffer> trace_buffer_;
+  std::unique_ptr<TraceConfig> trace_config_;
+  Mode mode_ = DISABLED;
+
+  // Disallow copy and assign
+  TracingController(const TracingController&) = delete;
+  void operator=(const TracingController&) = delete;
+};
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8
+
+#endif  // V8_LIBPLATFORM_V8_TRACING_H_

src/DEPS

@@ -22,5 +22,6 @@ include_rules = [
 specific_include_rules = {
   "d8\.cc": [
     "+include/libplatform/libplatform.h",
+    "+include/libplatform/v8-tracing.h",
   ],
 }

src/d8.cc

@@ -35,6 +35,7 @@
 #include "src/ostreams.h"
 
 #include "include/libplatform/libplatform.h"
+#include "include/libplatform/v8-tracing.h"
 #ifndef V8_SHARED
 #include "src/api.h"
 #include "src/base/cpu.h"
@@ -1991,6 +1992,9 @@ bool Shell::SetOptions(int argc, char* argv[]) {
         return false;
       }
       argv[i] = NULL;
+    } else if (strcmp(argv[i], "--enable-tracing") == 0) {
+      options.trace_enabled = true;
+      argv[i] = NULL;
     }
   }
 
@@ -2407,6 +2411,7 @@ static void DumpHeapConstants(i::Isolate* isolate) {
 
 
 int Shell::Main(int argc, char* argv[]) {
+  std::ofstream trace_file;
 #if (defined(_WIN32) || defined(_WIN64))
   UINT new_flags =
       SEM_FAILCRITICALERRORS | SEM_NOGPFAULTERRORBOX | SEM_NOOPENFILEERRORBOX;
@@ -2474,6 +2479,29 @@ int Shell::Main(int argc, char* argv[]) {
     Initialize(isolate);
     PerIsolateData data(isolate);
 
+    if (options.trace_enabled) {
+      trace_file.open("v8_trace.json");
+      platform::tracing::TracingController* tracing_controller =
+          new platform::tracing::TracingController();
+      platform::tracing::TraceBuffer* trace_buffer =
+          platform::tracing::TraceBuffer::CreateTraceBufferRingBuffer(
+              platform::tracing::TraceBuffer::kRingBufferChunks,
+              platform::tracing::TraceWriter::CreateJSONTraceWriter(
+                  trace_file));
+      platform::tracing::TraceConfig* trace_config;
+      trace_config = new platform::tracing::TraceConfig();
+      trace_config->AddIncludedCategory("v8");
+      tracing_controller->Initialize(trace_buffer);
+      tracing_controller->StartTracing(trace_config);
+#ifndef V8_SHARED
+      if (!i::FLAG_verify_predictable) {
+        platform::SetTracingController(g_platform, tracing_controller);
+      }
+#else
+      platform::SetTracingController(g_platform, tracing_controller);
+#endif
+    }
+
 #ifndef V8_SHARED
     if (options.dump_heap_constants) {
       DumpHeapConstants(reinterpret_cast<i::Isolate*>(isolate));

src/d8.h

@@ -290,7 +290,8 @@ class ShellOptions {
         isolate_sources(NULL),
         icu_data_file(NULL),
         natives_blob(NULL),
-        snapshot_blob(NULL) {}
+        snapshot_blob(NULL),
+        trace_enabled(false) {}
 
   ~ShellOptions() {
     delete[] isolate_sources;
@@ -318,6 +319,8 @@ class ShellOptions {
   const char* icu_data_file;
   const char* natives_blob;
   const char* snapshot_blob;
+  bool trace_enabled;
+  const char* trace_config;
 };
 
 #ifdef V8_SHARED

src/libplatform/default-platform.cc

@@ -29,11 +29,17 @@ bool PumpMessageLoop(v8::Platform* platform, v8::Isolate* isolate) {
   return reinterpret_cast<DefaultPlatform*>(platform)->PumpMessageLoop(isolate);
 }
 
+void SetTracingController(
+    v8::Platform* platform,
+    v8::platform::tracing::TracingController* tracing_controller) {
+  return reinterpret_cast<DefaultPlatform*>(platform)->SetTracingController(
+      tracing_controller);
+}
+
 const int DefaultPlatform::kMaxThreadPoolSize = 8;
 
 DefaultPlatform::DefaultPlatform()
-    : initialized_(false), thread_pool_size_(0) {}
-
+    : initialized_(false), thread_pool_size_(0), tracing_controller_(NULL) {}
 
 DefaultPlatform::~DefaultPlatform() {
   base::LockGuard<base::Mutex> guard(&lock_);
@@ -57,6 +63,11 @@ DefaultPlatform::~DefaultPlatform() {
       i->second.pop();
     }
   }
+
+  if (tracing_controller_) {
+    tracing_controller_->StopTracing();
+    delete tracing_controller_;
+  }
 }
 
 
@@ -173,15 +184,27 @@ uint64_t DefaultPlatform::AddTraceEvent(
     const char* scope, uint64_t id, uint64_t bind_id, int num_args,
     const char** arg_names, const uint8_t* arg_types,
     const uint64_t* arg_values, unsigned int flags) {
+  if (tracing_controller_) {
+    return tracing_controller_->AddTraceEvent(
+        phase, category_enabled_flag, name, scope, id, bind_id, num_args,
+        arg_names, arg_types, arg_values, flags);
+  }
+
   return 0;
 }
 
-
 void DefaultPlatform::UpdateTraceEventDuration(
-    const uint8_t* category_enabled_flag, const char* name, uint64_t handle) {}
-
+    const uint8_t* category_enabled_flag, const char* name, uint64_t handle) {
+  if (tracing_controller_) {
+    tracing_controller_->UpdateTraceEventDuration(category_enabled_flag, name,
+                                                  handle);
+  }
+}
 
 const uint8_t* DefaultPlatform::GetCategoryGroupEnabled(const char* name) {
+  if (tracing_controller_) {
+    return tracing_controller_->GetCategoryGroupEnabled(name);
+  }
   static uint8_t no = 0;
   return &no;
 }
@@ -193,6 +216,10 @@ const char* DefaultPlatform::GetCategoryGroupName(
   return dummy;
 }
 
+void DefaultPlatform::SetTracingController(
+    tracing::TracingController* tracing_controller) {
+  tracing_controller_ = tracing_controller;
+}
 
 size_t DefaultPlatform::NumberOfAvailableBackgroundThreads() {
   return static_cast<size_t>(thread_pool_size_);

src/libplatform/default-platform.h

@@ -10,6 +10,7 @@
 #include <queue>
 #include <vector>
 
+#include "include/libplatform/v8-tracing.h"
 #include "include/v8-platform.h"
 #include "src/base/macros.h"
 #include "src/base/platform/mutex.h"
@@ -22,6 +23,10 @@ class TaskQueue;
 class Thread;
 class WorkerThread;
 
+namespace tracing {
+class TracingController;
+}
+
 class DefaultPlatform : public Platform {
  public:
   DefaultPlatform();
@@ -54,7 +59,7 @@ class DefaultPlatform : public Platform {
                          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);
 
  private:
   static const int kMaxThreadPoolSize;
@@ -74,6 +79,7 @@ class DefaultPlatform : public Platform {
            std::priority_queue<DelayedEntry, std::vector<DelayedEntry>,
                                std::greater<DelayedEntry> > >
       main_thread_delayed_queue_;
+  tracing::TracingController* tracing_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(DefaultPlatform);
 };

src/libplatform/tracing/trace-buffer.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/libplatform/tracing/trace-buffer.h"
+
+namespace v8 {
+namespace platform {
+namespace tracing {
+
+TraceBufferRingBuffer::TraceBufferRingBuffer(size_t max_chunks,
+                                             TraceWriter* trace_writer)
+    : max_chunks_(max_chunks) {
+  trace_writer_.reset(trace_writer);
+  chunks_.resize(max_chunks);
+}
+
+TraceBufferRingBuffer::~TraceBufferRingBuffer() {}
+
+TraceObject* TraceBufferRingBuffer::AddTraceEvent(uint64_t* handle) {
+  base::LockGuard<base::Mutex> guard(&mutex_);
+  if (is_empty_ || chunks_[chunk_index_]->IsFull()) {
+    chunk_index_ = is_empty_ ? 0 : NextChunkIndex(chunk_index_);
+    is_empty_ = false;
+    auto& chunk = chunks_[chunk_index_];
+    if (chunk) {
+      chunk->Reset(current_chunk_seq_++);
+    } else {
+      chunk.reset(new TraceBufferChunk(current_chunk_seq_++));
+    }
+  }
+  auto& chunk = chunks_[chunk_index_];
+  size_t event_index;
+  TraceObject* trace_object = chunk->AddTraceEvent(&event_index);
+  *handle = MakeHandle(chunk_index_, chunk->seq(), event_index);
+  return trace_object;
+}
+
+TraceObject* TraceBufferRingBuffer::GetEventByHandle(uint64_t handle) {
+  base::LockGuard<base::Mutex> guard(&mutex_);
+  size_t chunk_index, event_index;
+  uint32_t chunk_seq;
+  ExtractHandle(handle, &chunk_index, &chunk_seq, &event_index);
+  if (chunk_index >= chunks_.size()) return NULL;
+  auto& chunk = chunks_[chunk_index];
+  if (!chunk || chunk->seq() != chunk_seq) return NULL;
+  return chunk->GetEventAt(event_index);
+}
+
+bool TraceBufferRingBuffer::Flush() {
+  base::LockGuard<base::Mutex> guard(&mutex_);
+  // This flushes all the traces stored in the buffer.
+  if (!is_empty_) {
+    for (size_t i = NextChunkIndex(chunk_index_);; i = NextChunkIndex(i)) {
+      if (auto& chunk = chunks_[i]) {
+        for (size_t j = 0; j < chunk->size(); ++j) {
+          trace_writer_->AppendTraceEvent(chunk->GetEventAt(j));
+        }
+      }
+      if (i == chunk_index_) break;
+    }
+  }
+  trace_writer_->Flush();
+  // This resets the trace buffer.
+  is_empty_ = true;
+  return true;
+}
+
+uint64_t TraceBufferRingBuffer::MakeHandle(size_t chunk_index,
+                                           uint32_t chunk_seq,
+                                           size_t event_index) const {
+  return static_cast<uint64_t>(chunk_seq) * Capacity() +
+         chunk_index * TraceBufferChunk::kChunkSize + event_index;
+}
+
+void TraceBufferRingBuffer::ExtractHandle(uint64_t handle, size_t* chunk_index,
+                                          uint32_t* chunk_seq,
+                                          size_t* event_index) const {
+  *chunk_seq = static_cast<uint32_t>(handle / Capacity());
+  size_t indices = handle % Capacity();
+  *chunk_index = indices / TraceBufferChunk::kChunkSize;
+  *event_index = indices % TraceBufferChunk::kChunkSize;
+}
+
+size_t TraceBufferRingBuffer::NextChunkIndex(size_t index) const {
+  if (++index >= max_chunks_) index = 0;
+  return index;
+}
+
+TraceBufferChunk::TraceBufferChunk(uint32_t seq) : seq_(seq) {}
+
+void TraceBufferChunk::Reset(uint32_t new_seq) {
+  next_free_ = 0;
+  seq_ = new_seq;
+}
+
+TraceObject* TraceBufferChunk::AddTraceEvent(size_t* event_index) {
+  *event_index = next_free_++;
+  return &chunk_[*event_index];
+}
+
+TraceBuffer* TraceBuffer::CreateTraceBufferRingBuffer(
+    size_t max_chunks, TraceWriter* trace_writer) {
+  return new TraceBufferRingBuffer(max_chunks, trace_writer);
+}
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8

src/libplatform/tracing/trace-buffer.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 SRC_LIBPLATFORM_TRACING_TRACE_BUFFER_H_
+#define SRC_LIBPLATFORM_TRACING_TRACE_BUFFER_H_
+
+#include <memory>
+#include <vector>
+
+#include "include/libplatform/v8-tracing.h"
+#include "src/base/platform/mutex.h"
+
+namespace v8 {
+namespace platform {
+namespace tracing {
+
+class TraceBufferRingBuffer : public TraceBuffer {
+ public:
+  TraceBufferRingBuffer(size_t max_chunks, TraceWriter* trace_writer);
+  ~TraceBufferRingBuffer();
+
+  TraceObject* AddTraceEvent(uint64_t* handle) override;
+  TraceObject* GetEventByHandle(uint64_t handle) override;
+  bool Flush() override;
+
+ private:
+  uint64_t MakeHandle(size_t chunk_index, uint32_t chunk_seq,
+                      size_t event_index) const;
+  void ExtractHandle(uint64_t handle, size_t* chunk_index, uint32_t* chunk_seq,
+                     size_t* event_index) const;
+  size_t Capacity() const { return max_chunks_ * TraceBufferChunk::kChunkSize; }
+  size_t NextChunkIndex(size_t index) const;
+
+  mutable base::Mutex mutex_;
+  size_t max_chunks_;
+  std::unique_ptr<TraceWriter> trace_writer_;
+  std::vector<std::unique_ptr<TraceBufferChunk>> chunks_;
+  size_t chunk_index_;
+  bool is_empty_ = true;
+  uint32_t current_chunk_seq_ = 1;
+};
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8
+
+#endif  // SRC_LIBPLATFORM_TRACING_TRACE_BUFFER_H_

src/libplatform/tracing/trace-config.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 <string.h>
+
+#include "include/libplatform/v8-tracing.h"
+#include "src/base/logging.h"
+
+namespace v8 {
+
+class Isolate;
+
+namespace platform {
+namespace tracing {
+
+bool TraceConfig::IsCategoryGroupEnabled(const char* category_group) const {
+  for (auto included_category : included_categories_) {
+    if (strcmp(included_category.data(), category_group) == 0) return true;
+  }
+  return false;
+}
+
+void TraceConfig::AddIncludedCategory(const char* included_category) {
+  DCHECK(included_category != NULL && strlen(included_category) > 0);
+  included_categories_.push_back(included_category);
+}
+
+void TraceConfig::AddExcludedCategory(const char* excluded_category) {
+  DCHECK(excluded_category != NULL && strlen(excluded_category) > 0);
+  excluded_categories_.push_back(excluded_category);
+}
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8

src/libplatform/tracing/trace-object.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 "include/libplatform/v8-tracing.h"
+
+#include "src/base/platform/platform.h"
+#include "src/base/platform/time.h"
+
+namespace v8 {
+namespace platform {
+namespace tracing {
+
+void TraceObject::Initialize(char phase, const uint8_t* category_enabled_flag,
+                             const char* name, const char* scope, uint64_t id,
+                             uint64_t bind_id, int num_args,
+                             const char** arg_names, const uint8_t* arg_types,
+                             const uint64_t* arg_values, unsigned int flags) {
+  pid_ = base::OS::GetCurrentProcessId();
+  tid_ = base::OS::GetCurrentThreadId();
+  phase_ = phase;
+  category_enabled_flag_ = category_enabled_flag;
+  name_ = name;
+  scope_ = scope;
+  id_ = id;
+  bind_id_ = bind_id;
+  num_args_ = num_args;
+  flags_ = flags;
+  ts_ = base::TimeTicks::HighResolutionNow().ToInternalValue();
+  tts_ = base::ThreadTicks::Now().ToInternalValue();
+  duration_ = 0;
+  cpu_duration_ = 0;
+}
+
+void TraceObject::UpdateDuration() {
+  duration_ = base::TimeTicks::HighResolutionNow().ToInternalValue() - ts_;
+  cpu_duration_ = base::ThreadTicks::Now().ToInternalValue() - tts_;
+}
+
+void TraceObject::InitializeForTesting(
+    char phase, const uint8_t* category_enabled_flag, const char* name,
+    const char* scope, uint64_t id, uint64_t bind_id, int num_args,
+    const char** arg_names, const uint8_t* arg_types,
+    const uint64_t* arg_values, unsigned int flags, int pid, int tid,
+    int64_t ts, int64_t tts, uint64_t duration, uint64_t cpu_duration) {
+  pid_ = pid;
+  tid_ = tid;
+  phase_ = phase;
+  category_enabled_flag_ = category_enabled_flag;
+  name_ = name;
+  scope_ = scope;
+  id_ = id;
+  bind_id_ = bind_id;
+  num_args_ = num_args;
+  flags_ = flags;
+  ts_ = ts;
+  tts_ = tts;
+  duration_ = duration;
+  cpu_duration_ = cpu_duration;
+}
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8

src/libplatform/tracing/trace-writer.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/libplatform/tracing/trace-writer.h"
+
+#include "src/base/platform/platform.h"
+
+namespace v8 {
+namespace platform {
+namespace tracing {
+
+JSONTraceWriter::JSONTraceWriter(std::ostream& stream) : stream_(stream) {
+  stream_ << "{\"traceEvents\":[";
+}
+
+JSONTraceWriter::~JSONTraceWriter() { stream_ << "]}"; }
+
+void JSONTraceWriter::AppendTraceEvent(TraceObject* trace_event) {
+  if (append_comma_) stream_ << ",";
+  append_comma_ = true;
+  if (trace_event->scope() == NULL) {
+    stream_ << "{\"pid\":" << trace_event->pid()
+            << ",\"tid\":" << trace_event->tid()
+            << ",\"ts\":" << trace_event->ts()
+            << ",\"tts\":" << trace_event->tts() << ",\"ph\":\""
+            << trace_event->phase() << "\",\"cat\":\""
+            << TracingController::GetCategoryGroupName(
+                   trace_event->category_enabled_flag())
+            << "\",\"name\":\"" << trace_event->name()
+            << "\",\"args\":{},\"dur\":" << trace_event->duration()
+            << ",\"tdur\":" << trace_event->cpu_duration() << "}";
+  } else {
+    stream_ << "{\"pid\":" << trace_event->pid()
+            << ",\"tid\":" << trace_event->tid()
+            << ",\"ts\":" << trace_event->ts()
+            << ",\"tts\":" << trace_event->tts() << ",\"ph\":\""
+            << trace_event->phase() << "\",\"cat\":\""
+            << TracingController::GetCategoryGroupName(
+                   trace_event->category_enabled_flag())
+            << "\",\"name\":\"" << trace_event->name() << "\",\"scope\":\""
+            << trace_event->scope()
+            << "\",\"args\":{},\"dur\":" << trace_event->duration()
+            << ",\"tdur\":" << trace_event->cpu_duration() << "}";
+  }
+  // TODO(fmeawad): Add support for Flow Events.
+}
+
+void JSONTraceWriter::Flush() {}
+
+TraceWriter* TraceWriter::CreateJSONTraceWriter(std::ostream& stream) {
+  return new JSONTraceWriter(stream);
+}
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8

src/libplatform/tracing/trace-writer.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 SRC_LIBPLATFORM_TRACING_TRACE_WRITER_H_
+#define SRC_LIBPLATFORM_TRACING_TRACE_WRITER_H_
+
+#include "include/libplatform/v8-tracing.h"
+
+namespace v8 {
+namespace platform {
+namespace tracing {
+
+class JSONTraceWriter : public TraceWriter {
+ public:
+  explicit JSONTraceWriter(std::ostream& stream);
+  ~JSONTraceWriter();
+  void AppendTraceEvent(TraceObject* trace_event) override;
+  void Flush() override;
+
+ private:
+  std::ostream& stream_;
+  bool append_comma_ = false;
+};
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8
+
+#endif  // SRC_LIBPLATFORM_TRACING_TRACE_WRITER_H_

src/libplatform/tracing/tracing-controller.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 <stdio.h>
+#include <string.h>
+
+#include "include/libplatform/v8-tracing.h"
+
+#include "src/base/platform/mutex.h"
+
+namespace v8 {
+namespace platform {
+namespace tracing {
+
+#define MAX_CATEGORY_GROUPS 200
+
+// Parallel arrays g_category_groups and g_category_group_enabled are separate
+// so that a pointer to a member of g_category_group_enabled can be easily
+// converted to an index into g_category_groups. This allows macros to deal
+// only with char enabled pointers from g_category_group_enabled, and we can
+// convert internally to determine the category name from the char enabled
+// pointer.
+const char* g_category_groups[MAX_CATEGORY_GROUPS] = {
+    "toplevel", "tracing already shutdown",
+    "tracing categories exhausted; must increase MAX_CATEGORY_GROUPS",
+    "__metadata"};
+
+// The enabled flag is char instead of bool so that the API can be used from C.
+unsigned char g_category_group_enabled[MAX_CATEGORY_GROUPS] = {0};
+// Indexes here have to match the g_category_groups array indexes above.
+const int g_category_already_shutdown = 1;
+const int g_category_categories_exhausted = 2;
+// Metadata category not used in V8.
+// const int g_category_metadata = 3;
+const int g_num_builtin_categories = 4;
+
+// Skip default categories.
+v8::base::AtomicWord g_category_index = g_num_builtin_categories;
+
+void TracingController::Initialize(TraceBuffer* trace_buffer) {
+  trace_buffer_.reset(trace_buffer);
+}
+
+uint64_t TracingController::AddTraceEvent(
+    char phase, const uint8_t* category_enabled_flag, const char* name,
+    const char* scope, uint64_t id, uint64_t bind_id, int num_args,
+    const char** arg_names, const uint8_t* arg_types,
+    const uint64_t* arg_values, unsigned int flags) {
+  uint64_t handle;
+  TraceObject* trace_object = trace_buffer_->AddTraceEvent(&handle);
+  if (trace_object) {
+    trace_object->Initialize(phase, category_enabled_flag, name, scope, id,
+                             bind_id, num_args, arg_names, arg_types,
+                             arg_values, flags);
+  }
+  return handle;
+}
+
+void TracingController::UpdateTraceEventDuration(
+    const uint8_t* category_enabled_flag, const char* name, uint64_t handle) {
+  TraceObject* trace_object = trace_buffer_->GetEventByHandle(handle);
+  if (!trace_object) return;
+  trace_object->UpdateDuration();
+}
+
+const uint8_t* TracingController::GetCategoryGroupEnabled(
+    const char* category_group) {
+  if (!trace_buffer_) {
+    DCHECK(!g_category_group_enabled[g_category_already_shutdown]);
+    return &g_category_group_enabled[g_category_already_shutdown];
+  }
+  return GetCategoryGroupEnabledInternal(category_group);
+}
+
+const char* TracingController::GetCategoryGroupName(
+    const uint8_t* category_group_enabled) {
+  // Calculate the index of the category group by finding
+  // category_group_enabled in g_category_group_enabled array.
+  uintptr_t category_begin =
+      reinterpret_cast<uintptr_t>(g_category_group_enabled);
+  uintptr_t category_ptr = reinterpret_cast<uintptr_t>(category_group_enabled);
+  // Check for out of bounds category pointers.
+  DCHECK(category_ptr >= category_begin &&
+         category_ptr < reinterpret_cast<uintptr_t>(g_category_group_enabled +
+                                                    MAX_CATEGORY_GROUPS));
+  uintptr_t category_index =
+      (category_ptr - category_begin) / sizeof(g_category_group_enabled[0]);
+  return g_category_groups[category_index];
+}
+
+void TracingController::StartTracing(TraceConfig* trace_config) {
+  trace_config_.reset(trace_config);
+  mode_ = RECORDING_MODE;
+  UpdateCategoryGroupEnabledFlags();
+}
+
+void TracingController::StopTracing() {
+  mode_ = DISABLED;
+  UpdateCategoryGroupEnabledFlags();
+  trace_buffer_->Flush();
+}
+
+void TracingController::UpdateCategoryGroupEnabledFlag(size_t category_index) {
+  unsigned char enabled_flag = 0;
+  const char* category_group = g_category_groups[category_index];
+  if (mode_ == RECORDING_MODE &&
+      trace_config_->IsCategoryGroupEnabled(category_group)) {
+    enabled_flag |= ENABLED_FOR_RECORDING;
+  }
+
+  // TODO(fmeawad): EventCallback and ETW modes are not yet supported in V8.
+  // TODO(primiano): this is a temporary workaround for catapult:#2341,
+  // to guarantee that metadata events are always added even if the category
+  // filter is "-*". See crbug.com/618054 for more details and long-term fix.
+  if (mode_ == RECORDING_MODE && !strcmp(category_group, "__metadata")) {
+    enabled_flag |= ENABLED_FOR_RECORDING;
+  }
+
+  g_category_group_enabled[category_index] = enabled_flag;
+}
+
+void TracingController::UpdateCategoryGroupEnabledFlags() {
+  size_t category_index = base::NoBarrier_Load(&g_category_index);
+  for (size_t i = 0; i < category_index; i++) UpdateCategoryGroupEnabledFlag(i);
+}
+
+const uint8_t* TracingController::GetCategoryGroupEnabledInternal(
+    const char* category_group) {
+  // Check that category groups does not contain double quote
+  DCHECK(!strchr(category_group, '"'));
+
+  // The g_category_groups is append only, avoid using a lock for the fast path.
+  size_t current_category_index = v8::base::Acquire_Load(&g_category_index);
+
+  // Search for pre-existing category group.
+  for (size_t i = 0; i < current_category_index; ++i) {
+    if (strcmp(g_category_groups[i], category_group) == 0) {
+      return &g_category_group_enabled[i];
+    }
+  }
+
+  unsigned char* category_group_enabled = NULL;
+  size_t category_index = base::Acquire_Load(&g_category_index);
+  for (size_t i = 0; i < category_index; ++i) {
+    if (strcmp(g_category_groups[i], category_group) == 0) {
+      return &g_category_group_enabled[i];
+    }
+  }
+
+  // Create a new category group.
+  // Check that there is a slot for the new category_group.
+  DCHECK(category_index < MAX_CATEGORY_GROUPS);
+  if (category_index < MAX_CATEGORY_GROUPS) {
+    // Don't hold on to the category_group pointer, so that we can create
+    // category groups with strings not known at compile time (this is
+    // required by SetWatchEvent).
+    const char* new_group = strdup(category_group);
+    g_category_groups[category_index] = new_group;
+    DCHECK(!g_category_group_enabled[category_index]);
+    // Note that if both included and excluded patterns in the
+    // TraceConfig are empty, we exclude nothing,
+    // thereby enabling this category group.
+    UpdateCategoryGroupEnabledFlag(category_index);
+    category_group_enabled = &g_category_group_enabled[category_index];
+    // Update the max index now.
+    base::Release_Store(&g_category_index, category_index + 1);
+  } else {
+    category_group_enabled =
+        &g_category_group_enabled[g_category_categories_exhausted];
+  }
+  return category_group_enabled;
+}
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8

src/v8.gyp

@@ -2004,10 +2004,18 @@
       ],
       'sources': [
         '../include/libplatform/libplatform.h',
+        '../include/libplatform/v8-tracing.h',
         'libplatform/default-platform.cc',
         'libplatform/default-platform.h',
         'libplatform/task-queue.cc',
         'libplatform/task-queue.h',
+        'libplatform/tracing/trace-buffer.cc',
+        'libplatform/tracing/trace-buffer.h',
+        'libplatform/tracing/trace-config.cc',
+        'libplatform/tracing/trace-object.cc',
+        'libplatform/tracing/trace-writer.cc',
+        'libplatform/tracing/trace-writer.h',
+        'libplatform/tracing/tracing-controller.cc',
         'libplatform/worker-thread.cc',
         'libplatform/worker-thread.h',
       ],

test/cctest/cctest.gyp

@@ -102,6 +102,7 @@
       'heap/test-mark-compact.cc',
       'heap/test-page-promotion.cc',
       'heap/test-spaces.cc',
+      'libplatform/test-tracing.cc',
       'libsampler/test-sampler.cc',
       'print-extension.cc',
       'profiler-extension.cc',

test/cctest/libplatform/test-tracing.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 <stdio.h>
+
+#include "include/libplatform/v8-tracing.h"
+#include "src/tracing/trace-event.h"
+#include "test/cctest/cctest.h"
+
+namespace v8 {
+namespace platform {
+namespace tracing {
+
+TEST(TestTraceConfig) {
+  LocalContext env;
+  TraceConfig* trace_config = new TraceConfig();
+  trace_config->EnableSampling();
+  trace_config->AddIncludedCategory("v8");
+  trace_config->AddIncludedCategory(TRACE_DISABLED_BY_DEFAULT("v8.runtime"));
+  trace_config->AddExcludedCategory("v8.cpu_profile");
+
+  CHECK_EQ(trace_config->IsSamplingEnabled(), true);
+  CHECK_EQ(trace_config->IsSystraceEnabled(), false);
+  CHECK_EQ(trace_config->IsArgumentFilterEnabled(), false);
+  CHECK_EQ(trace_config->IsCategoryGroupEnabled("v8"), true);
+  CHECK_EQ(trace_config->IsCategoryGroupEnabled("v8.cpu_profile"), false);
+  CHECK_EQ(trace_config->IsCategoryGroupEnabled("v8.cpu_profile.hires"), false);
+  CHECK_EQ(trace_config->IsCategoryGroupEnabled(
+               TRACE_DISABLED_BY_DEFAULT("v8.runtime")),
+           true);
+  delete trace_config;
+}
+
+TEST(TestTraceObject) {
+  TraceObject trace_object;
+  uint8_t category_enabled_flag = 41;
+  trace_object.Initialize('X', &category_enabled_flag, "Test.Trace",
+                          "Test.Scope", 42, 123, 0, NULL, NULL, NULL, 0);
+  CHECK_EQ('X', trace_object.phase());
+  CHECK_EQ(category_enabled_flag, *trace_object.category_enabled_flag());
+  CHECK_EQ(std::string("Test.Trace"), std::string(trace_object.name()));
+  CHECK_EQ(std::string("Test.Scope"), std::string(trace_object.scope()));
+  CHECK_EQ(0, trace_object.duration());
+  CHECK_EQ(0, trace_object.cpu_duration());
+}
+
+class MockTraceWriter : public TraceWriter {
+ public:
+  void AppendTraceEvent(TraceObject* trace_event) override {
+    events_.push_back(trace_event->name());
+  }
+
+  void Flush() override {}
+
+  std::vector<std::string> events() { return events_; }
+
+ private:
+  std::vector<std::string> events_;
+};
+
+TEST(TestTraceBufferRingBuffer) {
+  // We should be able to add kChunkSize * 2 + 1 trace events.
+  const int HANDLES_COUNT = TraceBufferChunk::kChunkSize * 2 + 1;
+  MockTraceWriter* writer = new MockTraceWriter();
+  TraceBuffer* ring_buffer =
+      TraceBuffer::CreateTraceBufferRingBuffer(2, writer);
+  std::string names[HANDLES_COUNT];
+  for (int i = 0; i < HANDLES_COUNT; ++i) {
+    names[i] = "Test.EventNo" + std::to_string(i);
+  }
+
+  std::vector<uint64_t> handles(HANDLES_COUNT);
+  uint8_t category_enabled_flag = 41;
+  for (size_t i = 0; i < handles.size(); ++i) {
+    TraceObject* trace_object = ring_buffer->AddTraceEvent(&handles[i]);
+    CHECK_NOT_NULL(trace_object);
+    trace_object->Initialize('X', &category_enabled_flag, names[i].c_str(),
+                             "Test.Scope", 42, 123, 0, NULL, NULL, NULL, 0);
+    trace_object = ring_buffer->GetEventByHandle(handles[i]);
+    CHECK_NOT_NULL(trace_object);
+    CHECK_EQ('X', trace_object->phase());
+    CHECK_EQ(names[i], std::string(trace_object->name()));
+    CHECK_EQ(category_enabled_flag, *trace_object->category_enabled_flag());
+  }
+
+  // We should only be able to retrieve the last kChunkSize + 1.
+  for (size_t i = 0; i < TraceBufferChunk::kChunkSize; ++i) {
+    CHECK_NULL(ring_buffer->GetEventByHandle(handles[i]));
+  }
+
+  for (size_t i = TraceBufferChunk::kChunkSize; i < handles.size(); ++i) {
+    TraceObject* trace_object = ring_buffer->GetEventByHandle(handles[i]);
+    CHECK_NOT_NULL(trace_object);
+    // The object properties should be correct.
+    CHECK_EQ('X', trace_object->phase());
+    CHECK_EQ(names[i], std::string(trace_object->name()));
+    CHECK_EQ(category_enabled_flag, *trace_object->category_enabled_flag());
+  }
+
+  // Check Flush(), that the writer wrote the last kChunkSize  1 event names.
+  ring_buffer->Flush();
+  auto events = writer->events();
+  CHECK_EQ(TraceBufferChunk::kChunkSize + 1, events.size());
+  for (size_t i = TraceBufferChunk::kChunkSize; i < handles.size(); ++i) {
+    CHECK_EQ(names[i], events[i - TraceBufferChunk::kChunkSize]);
+  }
+  delete ring_buffer;
+}
+
+TEST(TestJSONTraceWriter) {
+  std::ostringstream stream;
+  v8::Platform* old_platform = i::V8::GetCurrentPlatform();
+  v8::Platform* default_platform = v8::platform::CreateDefaultPlatform();
+  i::V8::SetPlatformForTesting(default_platform);
+  // Create a scope for the tracing controller to terminate the trace writer.
+  {
+    TracingController tracing_controller;
+    platform::SetTracingController(default_platform, &tracing_controller);
+    TraceWriter* writer = TraceWriter::CreateJSONTraceWriter(stream);
+
+    TraceBuffer* ring_buffer =
+        TraceBuffer::CreateTraceBufferRingBuffer(1, writer);
+    tracing_controller.Initialize(ring_buffer);
+    TraceConfig* trace_config = new TraceConfig();
+    trace_config->AddIncludedCategory("v8-cat");
+    tracing_controller.StartTracing(trace_config);
+
+    TraceObject trace_object;
+    trace_object.InitializeForTesting(
+        'X', tracing_controller.GetCategoryGroupEnabled("v8-cat"), "Test0",
+        v8::internal::tracing::kGlobalScope, 42, 123, 0, NULL, NULL, NULL, 0,
+        11, 22, 100, 50, 33, 44);
+    writer->AppendTraceEvent(&trace_object);
+    trace_object.InitializeForTesting(
+        'Y', tracing_controller.GetCategoryGroupEnabled("v8-cat"), "Test1",
+        v8::internal::tracing::kGlobalScope, 43, 456, 0, NULL, NULL, NULL, 0,
+        55, 66, 110, 55, 77, 88);
+    writer->AppendTraceEvent(&trace_object);
+    tracing_controller.StopTracing();
+  }
+
+  std::string trace_str = stream.str();
+  std::string expected_trace_str =
+      "{\"traceEvents\":[{\"pid\":11,\"tid\":22,\"ts\":100,\"tts\":50,"
+      "\"ph\":\"X\",\"cat\":\"v8-cat\",\"name\":\"Test0\",\"args\":{},"
+      "\"dur\":33,\"tdur\":44},{\"pid\":55,\"tid\":66,\"ts\":110,\"tts\":55,"
+      "\"ph\":\"Y\",\"cat\":\"v8-cat\",\"name\":\"Test1\",\"args\":{},\"dur\":"
+      "77,\"tdur\":88}]}";
+
+  CHECK_EQ(expected_trace_str, trace_str);
+
+  i::V8::SetPlatformForTesting(old_platform);
+}
+
+TEST(TestTracingController) {
+  v8::Platform* old_platform = i::V8::GetCurrentPlatform();
+  v8::Platform* default_platform = v8::platform::CreateDefaultPlatform();
+  i::V8::SetPlatformForTesting(default_platform);
+
+  TracingController tracing_controller;
+  platform::SetTracingController(default_platform, &tracing_controller);
+
+  MockTraceWriter* writer = new MockTraceWriter();
+  TraceBuffer* ring_buffer =
+      TraceBuffer::CreateTraceBufferRingBuffer(1, writer);
+  tracing_controller.Initialize(ring_buffer);
+  TraceConfig* trace_config = new TraceConfig();
+  trace_config->AddIncludedCategory("v8");
+  tracing_controller.StartTracing(trace_config);
+
+  TRACE_EVENT0("v8", "v8.Test");
+  // cat category is not included in default config
+  TRACE_EVENT0("cat", "v8.Test2");
+  TRACE_EVENT0("v8", "v8.Test3");
+  tracing_controller.StopTracing();
+
+  CHECK_EQ(2, writer->events().size());
+  CHECK_EQ(std::string("v8.Test"), writer->events()[0]);
+  CHECK_EQ(std::string("v8.Test3"), writer->events()[1]);
+
+  i::V8::SetPlatformForTesting(old_platform);
+}
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8