func (l LocalityID) ToString() (string, error) {
	b, err := json.Marshal(l)
	if err != nil {
		return "", err
	}
	return string(b), nil
}
ToString generates a string representation of LocalityID by marshalling it into
json. Not calling it String() so printf won't call it.
package internal
import (
	"encoding/json"
	"fmt"
	"google.golang.org/grpc/resolver"
)
type LocalityID struct {
	Region  string `json:"region,omitempty"`
	Zone    string `json:"zone,omitempty"`
	SubZone string `json:"subZone,omitempty"`
}