(Lori Stoll via AP)LOS ANGELES – Tom Petty once described him as one of rock music's most well-kept secrets, and Chris Hillman is fine with that. It was never about getting into the Rock and Roll Hall of Fame, either, although Hillman, McGuinn and their fellow Byrds are there, too. "I was just having so much fun.”That passion is revealed in his just-published memoir “Time Between: My Life as a Byrd, Burrito Brother, and Beyond." After moving on to another bluegrass ensemble he returned to Los Angeles, where he'd pick up the bass guitar this time and join the Byrds. He recently took part in a “car concert” at the Ventura County Fairgrounds but says that just wasn't the same.