Copy event label.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index bd3fe231eb0ce964c8447d190c655743f53c6ae9..901a4c8f7e557477fdc758ae0cdc238cd20371f5 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -5985,6 +5985,7 @@ DART_EXPORT void Dart_TimelineEvent(const char* label,
   if (event == NULL) {
     return;
   }
+  label = strdup(label);
   switch (type) {
     case Dart_Timeline_Event_Begin:
       event->Begin(label, timestamp0);
@@ -6013,6 +6014,7 @@ DART_EXPORT void Dart_TimelineEvent(const char* label,
     default:
       FATAL("Unknown Dart_Timeline_Event_Type");
   }
+  event->set_owns_label(true);
   event->SetNumArguments(argument_count);
   for (intptr_t i = 0; i < argument_count; i++) {
     event->CopyArgument(i, argument_names[i], argument_values[i]);