Reset code age when serializing code objects.

src/serialize.cc

Index: src/serialize.cc
diff --git a/src/serialize.cc b/src/serialize.cc
index 0cc629df780dcb7916f1ba6776fc4acce3906bf7..c28721900f7f7a96ff90ed5ea72e5cf939b62388 100644
--- a/src/serialize.cc
+++ b/src/serialize.cc
@@ -1991,6 +1991,7 @@ void CodeSerializer::SerializeObject(Object* o, HowToCode how_to_code,
           Code* lazy = *isolate()->builtins()->CompileLazy();
           SerializeBuiltin(lazy, how_to_code, where_to_point);
         } else {
+          code_object->MakeYoung();
           SerializeHeapObject(code_object, how_to_code, where_to_point);
         }
         return;