Heat olive oil in a large saucepan over medium heat. Cook onions 4-5 minutes, stirring occasionally. Add garlic and cook together until fragrant, 1-2 minutes.Place onions and garlic in crock and return pan to heat. Add ground beef and pork to pan and cook thoroughly, until no pink remains. Drain all but 2 tablespoons of grease, and place meat and remaining grease in crock.Add tomato sauce, beer, diced tomatoes, beans, corn, cocoa powder, and spices to crock and stir until everything is well distributed.Cook on low heat for 5-6 hours.