Not that they had to seal the deal to be the Oscars’ frontrunner for Best Original Song or anything. Lady Gaga and Bradley Cooper, co-stars and compliment givers of A Star Is Born, blew off some beautiful sonic steam after Cooper was snubbed for Best Director by reuniting at Gaga’s Las Vegas residency on Saturday night. Cooper’s appearance came as a surprise to the euphoric audience, and the duo, obviously, sung the film’s smash hit “Shallow” — the first time they ever performed it live. That husky Jackson Maine voice! That haunting vulnerability of Ally! Consider this a warm-up for whatever “unorthodox” performance they have planned for Oscars night.