func (samplerOptions) Metrics(m *Metrics) SamplerOption {
	return func(o *samplerOptions) {
		o.metrics = m
	}
}
Metrics creates a SamplerOption that initializes Metrics on the sampler,
which is used to emit statistics.
package jaeger
import (
	"time"
)
type SamplerOption func(options *samplerOptions)
var SamplerOptions samplerOptions
type samplerOptions struct {
	metrics                 *Metrics
	maxOperations           int
	sampler                 Sampler
	logger                  Logger
	samplingServerURL       string
	samplingRefreshInterval time.Duration
}