San Francisco's restaurateur-turned-mayor Gavin Newsom cast doubt Friday over the viability of a threat made by restaurant owners who said they might shut down for a day to highlight the rising cost of doing business in the city. Newsom, who sold his interest in such popular San Francisco spots as PlumpJack Cafe and Balboa Cafe before his 2004 swearing-in, said he could sympathize with recent concerns raised by the Golden Gate Restaurant Association, but said that a one-day closure would only hurt the restaurants and that a majority of them would probably not participate. "It's against their best interest," Newsom...