ARCADIA, Calif. – When Art Sherman went to the Kentucky Derby as the exercise rider for Swaps in 1955, he rode in a railroad boxcar. Now, six decades later, he has jetted to places like Dubai and London as the celebrated trainer of a celebrated horse, California Chrome. But as that run nears its end, Sherman reflected on what California Chrome has meant to him, marveling at the good fortune that came his way so late in his training career.