The two affected tests where playing until a specific
position to enable the player to read ahead. The method
pauses at exactly the target position, but then has
temporarily undetermined behavior because the playback
thread uses player.getClock().onThreadBlocked() that lets
the playback thread make progress in parallel to the test
thread. The tests were flaky because they sometimes made
so much progress that they ended playback before we could
query the updated renderer state.
This can be fixed by using
run(player).untilBackgroundThreadCondition instead, which
is guaranteed to be fully deterministic, but may not be able
to stop at exactly the desired position (which we don't
really need anyway for this test).
PiperOrigin-RevId: 634699752
34792f7b11