If a person dies intestate as to all or any part of his estate, property which he gave in his lifetime to an heir is treated as an advancement against the latter's share of the estate only if declared in a writing by the decedent or acknowledged in writing by the heir to be an advancement. For this purpose the property advanced is valued as of the time the heir came into possession or enjoyment of the property or as of the time of death of the decedent, whichever first occurs. If the recipient of the property fails to survive the decedent, the property is not taken into account in computing the intestate share to be received by the recipient's issue unless the declaration or acknowledgment so provides.