SDK / exoplayer

*** Reason for rollforward ***

Rollforward after making sure the handler is created,
and that a test is written preventing a
similar regression.

*** Original change description ***

Rollback of https://github.com/google/ExoPlayer/commit/b6f5a263f725089c026bb8416ade555f4f16a2bc

*** Original commit ***

Rollforward of commit 5612ac50.

*** Reason for rollforward ***

Rollforward after making sure the handler is created
from the playback thread and not from an app thread.

*** Original change description ***

Rollback of https://github.com/google/ExoPlayer/commit/e1beb1d1946bb8ca94f62578aee8cbadd97b6e2b

*** Original commit ***

PiperOrigin-RevId: 318274400