Currently there seems to be no way to get and set the scroll position of the webview. This was possible in webkit1 because the webview implemented the gtk scrollable interface and could be placed inside an scrolledwindow. It would be nice to have this functionality back with webkit2.
You can use JavaScript to get and set the scroll position. Using window.scrollTo(x,y) JS function and window.scrollX and window.scrollY properties. https://wiki.gnome.org/Projects/WebKitGtk/ProgrammingGuide/Cookbook#Scrolling
I think this can be closed now.