I would recommend consulting the Google Fonts docs or query for Chome bugs. All Asciidoctor html5 output does is load fonts from Google Fonts as recommended on the site.
Having said that, I am thinking that in a future version of Asciidoctor, we should use the web font loader script which not only gives us more control but also supports multiple providers. That would make it simpler to customize the font loading from the AsciiDoc document (fine-grained settings).
-Dan