Looks like Jason went to a party at Coachella with that girl.  There’s only one pic, but they are definitely holding hands.  And thanks to lienka for the heads up on more pics from Day 3 of the festival on Zimbio.com and also here.  British mags are saying she’s Rosie Huntington-Whitely and the photo agencies are saying Isabel Lucas.  I’m sure we’ll find out soon enough who is really is.