I just wasted a bunch of time trying to figure out why my Epiphany was using wpebackend-fdo 1.9.1 when I had built 1.9.90. Turns out webkit://gpu is presenting the version it was built against as if it were the version it is using at runtime. That's unhelpful.
Created attachment 425426 [details] Patch
Thanks for the patch. If this patch contains new public API please make sure it follows the guidelines for new WebKit2 GTK+ API. See https://trac.webkit.org/wiki/WebKitGTK/AddingNewWebKit2API
Comment on attachment 425426 [details] Patch Note that WPE port already does this nicely for libwpe... it's only a problem for GTK. (WPE port can't print the backend version because it has no way to do that, but GTK can because it always uses the fdo backend.)
Committed r275634: <https://commits.webkit.org/r275634> All reviewed patches have been landed. Closing bug and clearing flags on attachment 425426 [details].