On some devices, decoding gets stuck when the number of frames pending at the
`SurfaceTexture` is too high. We added a workaround that only allows one frame
to be pending at a time. That fixed the issue, however, based on on-device
testing it seems that it's safe to queue more than one frame.
Add a method that returns a safe estimate of the number of frames that can be
pending at a time, and use this to limit the number of frames that can be
released from the decoder but not processed by the frame processor chain.
PiperOrigin-RevId: 437057075
