A wildfire burning out of control in mountains and foothills east of Los Angeles mushroomed more than 50 percent overnight, forcing authorities to order three school districts to cancel classes due to heavy smoke and dangerous conditions. More than 900 firefighters were battling the so-called Pilot Fire, which has charred some 7,500 acres of bone-dry tinder and brush in the San Bernardino Mountains since it broke out around noon on Sunday.