How Grid display native row indexes

Please see  http://demo.vaadin.com/sampler/#ui/grids-and-trees/grid/item-editor , If the grid is sorted by NAME, the indexes are not displayed from 0 to 99 any more.

Is there any easy way for Grid to display native row indexes?

Those id's or indices are field in the bean, so when you change sort order, they go along. I.e. they are not native row row indices.
 

I don't think Grid exposes the native index in any API method available. You could file a ticket for enhancement: https://github.com/vaadin/framework/issues