[tracing] Support ConvertableToTraceFormat argument type.

src/libplatform/tracing/trace-writer.cc

Index: src/libplatform/tracing/trace-writer.cc
diff --git a/src/libplatform/tracing/trace-writer.cc b/src/libplatform/tracing/trace-writer.cc
index ec95527d5f6a892e4cc9437b5f526af471219830..7445087c565850395b89b0ddc9b78be764743563 100644
--- a/src/libplatform/tracing/trace-writer.cc
+++ b/src/libplatform/tracing/trace-writer.cc
@@ -7,6 +7,7 @@
 #include <cmath>
 
 #include "base/trace_event/common/trace_event_common.h"
+#include "include/v8-platform.h"
 #include "src/base/platform/platform.h"
 
 namespace v8 {
@@ -112,6 +113,12 @@ void JSONTraceWriter::AppendArgValue(uint8_t type,
   }
 }
 
+void JSONTraceWriter::AppendArgValue(ConvertableToTraceFormat* value) {
+  std::string arg_stringified;
+  value->AppendAsTraceFormat(&arg_stringified);
+  stream_ << arg_stringified;
+}
+
 JSONTraceWriter::JSONTraceWriter(std::ostream& stream) : stream_(stream) {
   stream_ << "{\"traceEvents\":[";
 }
@@ -143,10 +150,16 @@ void JSONTraceWriter::AppendTraceEvent(TraceObject* trace_event) {
   const char** arg_names = trace_event->arg_names();
   const uint8_t* arg_types = trace_event->arg_types();
   TraceObject::ArgValue* arg_values = trace_event->arg_values();
+  std::unique_ptr<v8::ConvertableToTraceFormat>* arg_convertables =
+      trace_event->arg_convertables();
   for (int i = 0; i < trace_event->num_args(); ++i) {
     if (i > 0) stream_ << ",";
     stream_ << "\"" << arg_names[i] << "\":";
-    AppendArgValue(arg_types[i], arg_values[i]);
+    if (arg_types[i] == TRACE_VALUE_TYPE_CONVERTABLE) {
+      AppendArgValue(arg_convertables[i].get());
+    } else {
+      AppendArgValue(arg_types[i], arg_values[i]);
+    }
   }
   stream_ << "}}";
   // TODO(fmeawad): Add support for Flow Events.