[tracing] Custom tag for the traceEvents array

This API will be used by Node.js to provide output compatible with
Chrome devtools.

Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I265495f8af39bfc78d7fdbe43ac308f0920e817d
Reviewed-on: https://chromium-review.googlesource.com/1044491Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Eugene Ostroukhov <eostroukhov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53041}

include/libplatform/v8-tracing.h

@@ -112,6 +112,8 @@ class V8_PLATFORM_EXPORT TraceWriter {
   virtual void Flush() = 0;
 
   static TraceWriter* CreateJSONTraceWriter(std::ostream& stream);
+  static TraceWriter* CreateJSONTraceWriter(std::ostream& stream,
+                                            const std::string& tag);
 
  private:
   // Disallow copy and assign

src/libplatform/tracing/trace-writer.cc

@@ -119,8 +119,12 @@ void JSONTraceWriter::AppendArgValue(ConvertableToTraceFormat* value) {
   stream_ << arg_stringified;
 }
 
-JSONTraceWriter::JSONTraceWriter(std::ostream& stream) : stream_(stream) {
-  stream_ << "{\"traceEvents\":[";
+JSONTraceWriter::JSONTraceWriter(std::ostream& stream)
+    : JSONTraceWriter(stream, "traceEvents") {}
+
+JSONTraceWriter::JSONTraceWriter(std::ostream& stream, const std::string& tag)
+    : stream_(stream) {
+  stream_ << "{\"" << tag << "\":[";
 }
 
 JSONTraceWriter::~JSONTraceWriter() { stream_ << "]}"; }
@@ -171,6 +175,11 @@ TraceWriter* TraceWriter::CreateJSONTraceWriter(std::ostream& stream) {
   return new JSONTraceWriter(stream);
 }
 
+TraceWriter* TraceWriter::CreateJSONTraceWriter(std::ostream& stream,
+                                                const std::string& tag) {
+  return new JSONTraceWriter(stream, tag);
+}
+
 }  // namespace tracing
 }  // namespace platform
 }  // namespace v8

src/libplatform/tracing/trace-writer.h

@@ -14,6 +14,7 @@ namespace tracing {
 class JSONTraceWriter : public TraceWriter {
  public:
   explicit JSONTraceWriter(std::ostream& stream);
+  JSONTraceWriter(std::ostream& stream, const std::string& tag);
   ~JSONTraceWriter();
   void AppendTraceEvent(TraceObject* trace_event) override;
   void Flush() override;

test/cctest/libplatform/test-tracing.cc

@@ -128,21 +128,15 @@ TEST(TestTraceBufferRingBuffer) {
   delete ring_buffer;
 }
 
-TEST(TestJSONTraceWriter) {
-  std::ostringstream stream;
-  // Create a scope for the tracing controller to terminate the trace writer.
-  {
+void PopulateJSONWriter(TraceWriter* writer) {
   v8::Platform* old_platform = i::V8::GetCurrentPlatform();
   std::unique_ptr<v8::Platform> default_platform(
       v8::platform::NewDefaultPlatform());
   i::V8::SetPlatformForTesting(default_platform.get());
-    auto tracing =
-        base::make_unique<v8::platform::tracing::TracingController>();
-    v8::platform::tracing::TracingController* tracing_controller =
-        tracing.get();
+  auto tracing = base::make_unique<v8::platform::tracing::TracingController>();
+  v8::platform::tracing::TracingController* tracing_controller = tracing.get();
   static_cast<v8::platform::DefaultPlatform*>(default_platform.get())
       ->SetTracingController(std::move(tracing));
-    TraceWriter* writer = TraceWriter::CreateJSONTraceWriter(stream);
 
   TraceBuffer* ring_buffer =
       TraceBuffer::CreateTraceBufferRingBuffer(1, writer);
@@ -164,8 +158,12 @@ TEST(TestJSONTraceWriter) {
   writer->AppendTraceEvent(&trace_object);
   tracing_controller->StopTracing();
   i::V8::SetPlatformForTesting(old_platform);
-  }
+}
 
+TEST(TestJSONTraceWriter) {
+  std::ostringstream stream;
+  TraceWriter* writer = TraceWriter::CreateJSONTraceWriter(stream);
+  PopulateJSONWriter(writer);
   std::string trace_str = stream.str();
   std::string expected_trace_str =
       "{\"traceEvents\":[{\"pid\":11,\"tid\":22,\"ts\":100,\"tts\":50,"
@@ -177,6 +175,21 @@ TEST(TestJSONTraceWriter) {
   CHECK_EQ(expected_trace_str, trace_str);
 }
 
+TEST(TestJSONTraceWriterWithCustomtag) {
+  std::ostringstream stream;
+  TraceWriter* writer = TraceWriter::CreateJSONTraceWriter(stream, "customTag");
+  PopulateJSONWriter(writer);
+  std::string trace_str = stream.str();
+  std::string expected_trace_str =
+      "{\"customTag\":[{\"pid\":11,\"tid\":22,\"ts\":100,\"tts\":50,"
+      "\"ph\":\"X\",\"cat\":\"v8-cat\",\"name\":\"Test0\",\"dur\":33,"
+      "\"tdur\":44,\"id\":\"0x2a\",\"args\":{}},{\"pid\":55,\"tid\":66,"
+      "\"ts\":110,\"tts\":55,\"ph\":\"Y\",\"cat\":\"v8-cat\",\"name\":"
+      "\"Test1\",\"dur\":77,\"tdur\":88,\"args\":{}}]}";
+
+  CHECK_EQ(expected_trace_str, trace_str);
+}
+
 TEST(TestTracingController) {
   v8::Platform* old_platform = i::V8::GetCurrentPlatform();
   std::unique_ptr<v8::Platform> default_platform(