[gin] Support ConvertableToTraceFormat arguments for events coming from V8.

gin/v8_platform.cc

Index: gin/v8_platform.cc
diff --git a/gin/v8_platform.cc b/gin/v8_platform.cc
index 15fb9f54ecf0fc3b576a83efe45c803dc2d7184c..51a096ccea3449842c23097fd84c33b9f9575d0d 100644
--- a/gin/v8_platform.cc
+++ b/gin/v8_platform.cc
@@ -97,11 +97,22 @@ uint64_t V8Platform::AddTraceEvent(char phase,
                                    const uint8_t* arg_types,
                                    const uint64_t* arg_values,
                                    unsigned int flags) {
+  std::unique_ptr<base::trace_event::ConvertableToTraceFormat> convertables[2];

[fmeawad, 2016/09/15 23:53:44]

Instead of the 2 if conditions, maybe a tiny for loop that we hope the compiler
will unroll?

[alph, 2016/09/15 23:58:14]

I doubt it will be able to unroll it as the num_args in not a compile time
constant.

+  if (num_args > 0 && arg_types[0] == TRACE_VALUE_TYPE_CONVERTABLE) {
+    convertables[0].reset(
+        reinterpret_cast<base::trace_event::ConvertableToTraceFormat*>(
+            arg_values[0]));
+  }
+  if (num_args > 1 && arg_types[1] == TRACE_VALUE_TYPE_CONVERTABLE) {
+    convertables[1].reset(
+        reinterpret_cast<base::trace_event::ConvertableToTraceFormat*>(
+            arg_values[1]));
+  }
   base::trace_event::TraceEventHandle handle =
       TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_BIND_ID(
           phase, category_enabled_flag, name, scope, id, bind_id, num_args,
-          arg_names, arg_types, (const long long unsigned int*)arg_values, NULL,
-          flags);
+          arg_names, arg_types, (const long long unsigned int*)arg_values,
+          convertables, flags);
   uint64_t result;
   memcpy(&result, &handle, sizeof(result));
   return result;