Before this CL, the video sink was stuck if a flush was executed:
- after VideoSink.onInputStreamChanged, which is setting
pendingInputStreamBufferPresentationTimeUs and
- before the previous stream was fully rendered.
This is because pendingInputStreamBufferPresentationTimeUs was not reset
to TIME_UNSET when flushing the sink, so that the sink was still waiting
for the last frame of the previous stream to be rendered in
handleInputFrame/Bitmap.
PiperOrigin-RevId: 667924517
a4d0735d4c