The world’s largest full-service restaurant company has also been one of the best, or at least most consistent, performers in the food industry in recent years. High expectations can have negative consequences, though, and Darden Restaurants shares were tumbling Thursday morning, on pace for their sharpest retreat in nearly two years. Revenue grew by 6.8% overall in Darden’s fiscal third quarter, but that was all due to restaurant openings and the acquisition of steakhouse chain Ruth’s Chris.