CHICAGO — Seven teenagers were arrested Wednesday in the beating and robbery of a 17-year-old Chicago high school student that was filmed and posted online, city police said. One of the teens was charged as an adult and the rest — a 15-year-old girl, two 16-year-old boys and three 15-year-old boys — were cited in juvenile delinquency petitions. All were charged with one count each of robbery and aggravated battery, police spokesman Mike Sullivan said.