SDK / exoplayer

Suggested during the review of https://github.com/google/ExoPlayer/commit/437d1b6e9ae1e085583b3ab8e8d686d1eea32b65

This keeps the Runnable -> Callable<Boolean> conversion encapsulated
inside SessionPlayerConnector which makes it clearer why it's needed.

PiperOrigin-RevId: 321553744