In a 3- or 4-qt. slow cooker, combine the first 8 ingredients. Add chicken and ale; toss to coat. Cook, covered, on low until chicken is tender, 6-8 hours. Remove meat; when cool enough to handle, shred with 2 forks., Strain cooking juices; skim fat. Transfer juices to a small saucepan; bring to a boil. In a small bowl, mix cornstarch and water until smooth; stir into saucepan. Return to a boil, stirring constantly; cook and stir until thickened, about 5 minutes. Add chicken to the sauce; toss to coat. Serve on buns. Add pickles and additional Sriracha sauce if desired.