Heat oven to 350. Spray bottom only of a 13x9 pan. In large bowl, beat cake mix, root beer, oil and egg whites with mixer on low sped 30 sec. then on med. speed 2 min., scraping bowl. Pour into pan. Bake 32 to 36 min. Cool Completely in pan about 1 hour. Stir in root beer concentrate or syrup into frosting, spread over cake. Just before serving sprinkle with crushed candies on top. Store loosely. NOTE: Candies will melt 1 to 3 hours after sprinkled on cake.