Dunkin' Donuts partnered with its sister brand, Baskin-Robbins, to introduce two new flavors of iced coffee inspired by Baskin-Robbins ice cream. The new flavors, available through the summer are Dunkin' Donuts' Mint Chocolate Chip Iced Coffee and Old Fashioned Butter Pecan. Dunkin' Donuts is offering a Twitter sweepstakes through Friday, April 5. Each day, the brand will ask a new trivia question about either Baskin-Robbins or iced coffee.