[Tracing] Expose trace serialization as part of tracing interface

include/libplatform/v8-tracing.h

Index: include/libplatform/v8-tracing.h
diff --git a/include/libplatform/v8-tracing.h b/include/libplatform/v8-tracing.h
index 7646ea5489664300ec7ad64ea1dbce6451c15424..a60d6fa77b613cc81011959a825f58043fef3daa 100644
--- a/include/libplatform/v8-tracing.h
+++ b/include/libplatform/v8-tracing.h
@@ -246,6 +246,20 @@ class TracingController {
   void operator=(const TracingController&) = delete;
 };
 
+class TraceSerializer {
+ public:
+  explicit TraceSerializer(std::ostream& stream);
+  void WritePrefix();
+  void AppendTraceEvent(TraceObject* trace_event);
+  void WriteSuffix();
+
+ private:
+  void AppendArgValue(uint8_t type, TraceObject::ArgValue value);
+
+  std::ostream& stream_;
+  bool append_comma_ = false;
+};
+
 }  // namespace tracing
 }  // namespace platform
 }  // namespace v8