SDK / exoplayer

At this point the only reason preventing the chunk package
from using RollingSampleBuffer directly, rather than
DefaultTrackOutput, is that the latter maintains the largest
parsed timestamp. This will be pushed inside the former in
the next CL. Following that, splicing logic will also be
pushed inside of RollingSampleBuffer, and HLS will be moved
over to using a single RollingSampleBuffer per track, with
the splicing done inline.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=120206658