code: func (h *Histogram) Export() *Snapshot {
  	return &Snapshot{
  		LowestTrackableValue:  h.lowestTrackableValue,
  		HighestTrackableValue: h.highestTrackableValue,
  		SignificantFigures:    h.significantFigures,
  		Counts:                append([]int64(nil), h.counts...), // copy
  	}
  }
docs: // Export returns a snapshot view of the Histogram. This can be later passed to
  // Import to construct a new Histogram with the same state.