Red Hot Chili Peppers and Chickenfoot drummer Chad Smith appeared on the "Tonight Show with Jimmy Fallon" Thursday night for a long awaited drum-off with Will Ferrell, the comedian that has long been said to look like Smith.   Smith and Ferrell sat for an interview with Fallon, Ferrell's former co-cast member on "Saturday Night Live," with each assuming the other's role.  The two men then took part in a traditional drum-off, though Ferrell's parts were actually being played by Questlove, the frontman of The Roots, the official house band for the show.  Folowing the drum-off, the rest of the Red Hot Chili Peppers showed up for their first performance on a late night talk show since 2006, while Ferrell switched over to play the cowbell in tribute to his iconic "VH1 Behind the Music" sketch on SNL years ago.  After the performance, Fallon declared Ferrell as the winner and presented him with a golden cowbell.