[Tracing] Expose trace serialization as part of tracing interface

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>
@@ skipping 228 matching lines @@
 
   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;
 };
 
+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
 
 #endif  // V8_LIBPLATFORM_V8_TRACING_H_