Cleanup after inobject slack tracking improvement.

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index d783d244129d58a8ce2eb1675764b114dd2adb4b..b665daaa567a2e763934bce2bfacd52535e183b1 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -469,6 +469,8 @@ Handle<JSFunction> Genesis::CreateEmptyFunction(Isolate* isolate) {
         factory->NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
     object_fun->set_initial_map(*object_function_map);
     object_function_map->set_constructor(*object_fun);
+    object_function_map->set_unused_property_fields(
+        JSObject::kInitialUnusedPropertiesCount);
 
     native_context()->set_object_function(*object_fun);