[strong] Implement revised strong class semantics

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 5f098148664ff86253602185809b89e27becb2a0..3ef6c99351d0b3d00c28b9879746e0362d55ecad 100644
--- a/src/runtime/runtime-classes.cc
+++ b/src/runtime/runtime-classes.cc
@@ -142,13 +142,6 @@ static MaybeHandle<Object> DefineClass(Isolate* isolate, Handle<Object> name,
       THROW_NEW_ERROR(isolate, NewTypeError(MessageTemplate::kStrongExtendNull),
                       Object);
     }
-  } else {
-    if (Handle<HeapObject>::cast(super_class)->map()->is_strong()) {
-      // Weak class is not permitted to extend strong class.
-      THROW_NEW_ERROR(isolate,
-                      NewTypeError(MessageTemplate::kStrongWeakExtend, name),
-                      Object);
-    }
   }
   Map::SetPrototype(map, prototype_parent);
   map->SetConstructor(*constructor);