Unbeknownst to many, Britney, Ke$ha, Carly Rae Jepsen and a cabal of their pop star comrades share a secret weapon: Her name is Bonnie McKee, and she's got an uncanny knack for crafting massive hits. Though she flirted with solo performance, the songwriter shines behind the scenes, concocting smash singles that offset moody vibes with danceable beats.