new classes: implement new.target passing to superclass constructor.

src/runtime/runtime-classes.cc

Index: src/runtime/runtime-classes.cc
diff --git a/src/runtime/runtime-classes.cc b/src/runtime/runtime-classes.cc
index ffd121e612ef4d3dd6572ce7dff205cf02139153..077c3d5abee68d05655f5f87a7d053d1864633a1 100644
--- a/src/runtime/runtime-classes.cc
+++ b/src/runtime/runtime-classes.cc
@@ -117,7 +117,7 @@ RUNTIME_FUNCTION(Runtime_DefineClass) {
   constructor->shared()->set_name(*name_string);
 
   if (FLAG_experimental_classes) {
-    if (!super_class->IsTheHole() && !super_class->IsNull()) {
+    if (!super_class->IsTheHole()) {
       Handle<Code> stub(isolate->builtins()->JSConstructStubForDerived());
       constructor->shared()->set_construct_stub(*stub);
     }