The reward offered in a rock-throwing incident that injured two traveling University of Oregon students last month has been more than doubled. The families of Molly Grabill, 20, and Chris Brewer, 19, are now asking $2,500 for help finding whoever was responsible for throwing a rock from an Interstate 5 overpass and causing a car to crash just south of Rice Hill. Grabill was driving a 1997 Subaru Legacy at 10:40 p.m. Nov. 26 under the Isadore Road overpass at Exit 146 when a baseball-sized rock crashed through the front windshield, striking her in the face. Brewer grabbed the steering …