tonihei 29208ec1ed Define CueGroup.EMPTY_TIME_ZERO for convenience
We create an empty CueGroup in many places as default or
where none is needed. Instead, we can define a constant
for this purpose and reuse it.

PiperOrigin-RevId: 467944841
2022-10-19 18:30:47 +00:00
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2022-10-19 18:19:27 +00:00