Zac Efron was two movies deep into the Disney Channel’s “High School Musical” franchise, in which he played singing, dancing basketball phenom Troy Bolton. He’d been the swoony romantic lead in the movie musical “Hairspray,” opposite John Travolta and Michelle Pfeiffer, was shortly to play opposite Matthew Perry in “17 Again,” and had pulled his T-shirt up on the cover of Rolling Stone under the headline “The New American Heartthrob.” At 21, Efron might have seemed like the kind of actor who was as likely to watch footage of the moon landing and decide to become an astronaut as he was to take inspiration from Mickey Rourke’s grizzled, broken-down performance. And yet.