Also mark as prototype when passing in while creating a function.

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index a844bd1cdb8ba274888cb87419830fc2122ddec8..e3a19a1e4ba988a0b19b00219e8ed50d83cb3a23 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -1268,6 +1268,11 @@ Handle<JSFunction> Factory::NewFunction(Handle<String> name,
       ? isolate()->sloppy_function_with_readonly_prototype_map()
       : isolate()->sloppy_function_map();
   Handle<JSFunction> result = NewFunction(map, name, code);
+  if (!prototype->IsTheHole()) {
+    Handle<JSObject> js_proto = Handle<JSObject>::cast(prototype);
+    Handle<Map> new_map = Map::CopyAsPrototypeMap(handle(js_proto->map()));
+    JSObject::MigrateToMap(js_proto, new_map);
+  }
   result->set_prototype_or_initial_map(*prototype);
   return result;
 }