Vanessa Arteaga sat at the “Danger Arena” game at Harrah’s Atlantic City with a controller in hand, shooting at robots as they jumped from behind walls. With each successful shot, the robot burst into an orange plume of flames. But Arteaga wasn’t just playing a video game. She was gambling. Harrah’s debuted the country’s first skill-based gambling machine, developed by GameCo Inc., on Wednesday, the latest attempt by an industry to attract younger gamblers by offering them something outside the scope of traditional slot machines.