Events are things that happen in the tracer such as a trace being dropped or
a span being started. These are counted and submitted as metrics.
const (
SpanStarted Event = iota SpansFinished
TracesDropped
DroppedP0Traces
DroppedP0Spans
PartialTraces
// Read-only. We duplicate some of the stats so that we can send them to the// agent in headers as well as counting them with statsd. AgentDroppedP0Traces
AgentDroppedP0Spans
)