A MessageObject is a purely internal object to hold information about

src/factory.h

Index: src/factory.h
diff --git a/src/factory.h b/src/factory.h
index a5e159123847f077d05e37317f98903810ba81a5..ba2b181a34ec983fd879e884543f6fb74c6a8ed7 100644
--- a/src/factory.h
+++ b/src/factory.h
@@ -365,6 +365,15 @@ class Factory : public AllStatic {
       Handle<SerializedScopeInfo> scope_info);
   static Handle<SharedFunctionInfo> NewSharedFunctionInfo(Handle<String> name);
 
+  static Handle<JSMessageObject> NewJSMessageObject(
+      Handle<String> type,
+      Handle<JSArray> arguments,
+      int start_position,
+      int end_position,
+      Handle<Object> script,
+      Handle<Object> stack_trace,
+      Handle<Object> stack_frames);
+
   static Handle<NumberDictionary> DictionaryAtNumberPut(
       Handle<NumberDictionary>,
       uint32_t key,