Combine ground round and onion in a large saucepan over medium-high heat. Cook, stirring, until beef is browned, about 5 minutes.
Transfer cooked beef and onions to slow cooker. Stir in water, tomatoes, kidney beans, black beans, corn, chocolate chips, chili powder, cumin, oregano, and salt. Cook on High until chili begins to bubble, about 20 minutes. Reduce heat to Low, and cook until thick, about 2 hours.
