new classes: special construct stub for derived classs and TDZ for `this`.

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 00567d432330e0e329e1ffd6b15b0c690f7c103d..846fd1aebdc40953ca52b0f205ab8a4010d6ef8f 100644
--- a/src/runtime/runtime-classes.cc
+++ b/src/runtime/runtime-classes.cc
@@ -107,6 +107,13 @@ RUNTIME_FUNCTION(Runtime_DefineClass) {
                                    : isolate->factory()->empty_string();
   constructor->shared()->set_name(*name_string);
 
+  if (FLAG_experimental_classes) {
+    if (!super_class->IsTheHole() && !super_class->IsNull()) {
+      Handle<Code> stub(isolate->builtins()->JSConstructStubForDerived());
+      constructor->shared()->set_construct_stub(*stub);
+    }
+  }
+
   JSFunction::SetPrototype(constructor, prototype);
   PropertyAttributes attribs =
       static_cast<PropertyAttributes>(DONT_ENUM | DONT_DELETE | READ_ONLY);