Preheat oven to 350°.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, baking soda, and salt in a large bowl.
Beat butter and brown sugar with a mixer at medium speed until light and fluffy; gradually add granulated sugar, beating well. Add cocoa and egg whites, beating well. Gradually add flour mixture, beating until blended. Stir in chocolate mini-chips.
Drop by rounded teaspoonfuls 1 1/2 inches apart onto baking sheets coated with cooking spray. Bake at 350° for 10 minutes. Cool on pans 2 minutes or until firm. Remove cookies from pans; cool completely on wire racks.