Preheat oven to 350. Combine flour, cocoa, baking soda, and salt in small bowl. Beat butter, sugar, brown sugar, and vanilla in large bowl until creamy. Add egg whites, one at a time, beating well after each addition. Gradually beat in flour mixture. Stir in chips. Drop by well-rounded teaspoon onto ungreased baking sheets. Bake for 9-11 minutes or until centers are set. Cool on baking sheet for 2 minutes, then move to cooling racks.