Justin Bieber 's a main draw for fans at Coachella this year ... and Chanel West Coast and Lexy Panterra really want people to go to the bathroom at a port-a-potty before the show -- not on the ground during it! We caught up with the stars at the Grow & Glow festival by Victoria Jancke near the main festival grounds Friday ... and we had to know what they were most excited to see at this year's event. Chanel immediately says the Biebs ... remembering him from when he showed up at Rob Dyrdek 's