Niners right guard Joe Looney, the lone remaining member of the 49ers’ disastrous seven-man 2012 draft class, was inactive Saturday for the first time this season. Looney, a fourth-round pick, was sidelined against the Chargers after he earned an unfavorable review from offensive coordinator Greg Roman on Thursday on the heels of the third start of his NFL career. In Looney’s spot, Dillon Farrell, an undrafted rookie from New Mexico, assumed his spot as the backup interior lineman. Right tackle Jonathan Martin returned to his backup role as Anthony Davis started Saturday for the first time since he suffered a concussion against the Giants on Nov.