Grease 2 (9-inch) round cake pans with cooking spray.Add brownie chunks into the pans.
In a large bowl,cake mix,pudding mix,egg whites,milk,oil,coconut extract and chocolate syrup with electric mixer on low speed 1 minute.Beat on medium speed 2 minutes.Fold in chocolate chips and brownie brittles.Pour batter into prepared pans.
Bake 30 to 32 minutes or until a toothpick inserted in center comes out clean.Cool 10 minutes.Remove cakes from pans to cooling racks;cool completely.Wrap cake layers;refrigerate at least 1 hour.
For Brownie Batter Frosting:in a medium bowl,stir whipped topping,cream cheese,brownie batter,heavy cream and 1/2 cup chocolate syrup with whisk until well blended;set aside.
Place 1 cake layer,top side up,on serving plate.Spread with half of the frosting mixture;sprinkle with brownie chunks.Place second cake layer,top side up,on brownie chunks.Spread remaining frosting mixture on top and sides of the cake.
Cover;refrigerate until serving time.Drizzle with remaining chocolate syrup over top of cake.Garnish with crushed brownie brittles.