By Mark Lamport-Stokes PACIFIC PALISADES, California (Reuters) - A year after losing a playoff for the Northern Trust Open, American Dustin Johnson was back in contention for the title as he ended the second round on Friday just two strokes off the lead. Johnson, a nine-times winner on the PGA Tour, took advantage of good scoring conditions at a sunny Riviera Country Club, firing 66 for an eight-under total of 134, two strokes behind leader Jason Kokrak. More...