The ExoPlayerImpl implementation forwards the stop request with this optional
parameter. To ensure correct masking (e.g. when timeline updates arrive after
calling reset in ExoPlayerImpl but before resetInternal in
ExoPlayerImplInternal), we use the existing prepareAck counter and extend it
also count stop operations. For this to work, we also return the updated
empty timeline after finishing the reset.
The CastPlayer doesn't support the two reset options so far.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177132107
f46cb907b7