NEW YORK — The warning came just moments too late: A man who had shot his ex-girlfriend a few hours earlier had traveled to New York City and vowed online to shoot two “pigs” in retaliation for the police chokehold death of Eric Garner. Just minutes before a wanted poster for Ismaaiyl Brinsley arrived in the NYPD’s Real Time Crime Center, he ambushed two officers in their patrol car in broad daylight, fatally shooting them before killing himself inside a subway station. Brinsley, 28, wrote on an Instagram account before Saturday’s shootings: “I’m putting wings on pigs today.