[profiler] Normalize time fields in the format.

[profiler] Normalize time fields in the format.

All events now come with a time field right after the event byte, and it is
encoded in the same way for all events (based on LogBuffer.time_base).

This allows readers to queue up events until a sync point event, then sort all
of those events by time, and process them in the order they were actually
written in.