The structure in fromkeith repo was changed, I don't think merging will work. Also I don't see any working example in his repo, unfortunately. If you know a bit of C it shouldn't be much of a hassle to add downloads supports to original cef2go repo. To add a default download handler, there is no need to expose any API to Go. It's just a matter of calling
callback->Continue(suggested_name, true); in CefDownloadHandler::OnBeforeDownload. Download handler needs to be implemented here:
https://github.com/CzarekTomczak/cef2go/blob/master/handlers/cef_client.h#L48 and then the OnBeforeDownload callback. You can take a look at fromkeith repo for reference, but most of its code that exposes API can be ignored. Patches/pull requests are welcome.