The clandestine sharing of gun buyers’ identities — without their knowledge and consent — marked a significant departure for an industry that has long prided itself on thwarting efforts to track who owns firearms in America. At least 10 gun industry businesses, including Glock, Smith & Wesson, Remington, Marlin and Mossberg, handed over names, addresses and other private data to the gun industry’s chief lobbying group, the National Shooting Sports Foundation.