D.C.-based Homesnap, the maker of a mobile app that allows users to find real estate data by taking photos of homes, has signed a deal that could be worth up to $15 million a year to provide 44,000 Washington area agents with customized residential sales information. The new application, called Homesnap Pro, connects brokers with critical information on commissions, tours and real-time social- network-like access to customers, colleagues and employers.