MediaPlayer2: address API council comments

Test: cts
Bug: 126700359
Bug: 126701061
Bug: 126701365
Bug: 126701652
Bug: 126701657
Bug: 126701901
Bug: 126702124
Bug: 126702181
Bug: 126702182
Change-Id: I3b33d7c1a403b6d2c13b93e5937a0f1a3e4d80a1