Preventive examination of a 28-year-old male patient revealed reddish smooth patches in form of different-sized circles on the back of tongue. The patches are circumscribed with a narrow whitish stripe. It is known that these tongue changes are not permanent, show up and disappear throughout a few years and don't bother him. The patient has a history of chronic gastritis. Histological examination of the epithelium revealed hyper- and parakeratosis. What is the most likely diagnosis?