Whenever any donation of real property has been made to a city or county for museum or art gallery purposes, or any building or improvements therefor have been erected upon public lands by an individual or corporation without cost to the city or county, the governing body of the city or county may delegate the management, operation, maintenance and regulation thereof to the donor or his successors, or to boards of trustees or directors nominated by the donor and appointed by the governing body of the city or county, upon such terms and conditions as the governing body may prescribe.