Rock & roll legends Aerosmith were joined onstage by actor Johnny Depp this week when the band performed at the famous Hollywood Bowl amphitheatre in Los Angeles.  The actor, who has been spreading his musical wings this year on a project with Jack White, helped out with guitar on Aerosmith's classic, "Train Kept a-Rollin."  Fan-filmed footage of the performance was posted online on Wednesday, and can be viewed below.  Depp previously performed with Aerosmith at the release party for his "Dark Shadows" film, and has also performed with White and even Marilyn Manson.  Depp also has a guest spot on Aerosmith's new allbum, "Music from Another Dimension!," which hits stores in November, and provided backing vocals for a Joe Perry song entitled "Freedom Fighter" which Perry says will be on an upcoming album or as a bonus track on a deluxe edition of a future set.