Dimmed lights and colonial-style balconies give little indication that trendy Shanghai eatery Atto Primo is part of global fast-food giant Yum Brands Inc (YUM.N), owner of the KFC and Pizza Hut brands. Overlooking Shanghai’s iconic riverside Bund and rubbing shoulders with the city’s most expensive venues, the restaurant is what Yum calls a “lab” where it studies Chinese diners as it looks to bounce back from a lengthy slump in its top market.