ClearAndLeak() is deprecated and will be removed.  The way to go about it is to make `NanUnsafePersistent<T>` subclass `Persistent<T, CopyablePersistentTraits<T> >` (PersistentBase in v3.24) where CopyablePersistentTraits is a template class that you implement yourself.  See NonCopyablePersistentTraits in v8.h for an example.