MELBOURNE — • It’s been more than two years since a WTA player won back-to-back majors, the eight Slams all yielding eight different champ. But Naomi Osaka is bidding to end this streak. The 2018 U.S. Open winner is seeded fourth here, hasn’t dropped a set, and betrays a firm sense of self-belief that wasn’t in evidence six months ago. Today she played crisply, overcame a few loose games and rolled into the third round, beating Tamara Zidansek 6-2, 6-4. There’s so much to like about Osaka, but high on the list: her commitment to tennis and indifference to celebrity.