func (b *ExponentialBackOff) GetElapsedTime() time.Duration {
	return b.Clock.Now().Sub(b.startTime)
}
func (b *ExponentialBackOff) GetElapsedTime() time.Duration {
	return b.Clock.Now().Sub(b.startTime)
}
// GetElapsedTime returns the elapsed time since an ExponentialBackOff instance
// is created and is reset when Reset() is called.
//
// The elapsed time is computed using time.Now().UnixNano().