onDismissed

Called on the main thread when the user puts the notification away (#427): a swipe, or removing the application from the recent apps screen while the player is not playing. The library has already paused the player and removed the notification, as it does without a callback; the reason tells a swipe from a press of pause, which also ends at Paused, so an application that reads a swipe as "I am done" can close the player and free what it holds. Removing the application while it plays leaves the sound going and calls nothing.