New-school troubadour Jon Bellion might be best known for “All Time Low,” his glitchy breakup song that hit big in 2016. Behind the scenes, though, he’s helped write glittery, hooky songs for some of pop’s biggest names, like Miley Cyrus’ roller-disco mood piece “Midnight Sky,” Christina Aguilera’s storming Demi Lovato collab “Fall in Line,” and Justin Bieber’s gospel-tinged Chance the Rapper duet “Holy.”