I don’t know “Page Previews” search option existed before under Google Search options, but now for me Page Previews option appearing under search tools in all browsers.I have also seen Google showing full page previews for their search results with magnifying glass effect recently.When we selected a search result page preview will be shown,page previews will be shown for all search results on that page as you navigate down with down arrow.

page previews

full page preview for searh results

full page previews for search results