The San Francisco 49ers have announced a contract extension for one of their best players.Defensive lineman Justin Smith, who turns 34 on Sept. 30 and is coming off triceps surgery, is now signed through the 2015 season. His contract was previously set to expire following the 2013 season.2011-12 DL Snaps Counting PlayoffsIt's not yet clear whether this contract extension means much in relation to how long Smith will factor along the defensive line.