func MonotonicEndTime(start time.Time) time.Time {
	return start.Add(time.Now().Sub(start))
}
MonotonicEndTime returns the end time at present
but offset from start, monotonically.

The monotonic clock is used in subtractions hence
the duration since start added back to start gives
end as a monotonic time.
See https://golang.org/pkg/time/#hdr-Monotonic_Clocks
package internal  
import (
	"fmt"
	"time"
	opencensus "go.opencensus.io"
)
var UserAgent = fmt.Sprintf("opencensus-go/%s", opencensus.Version())