fetch method
Implementation
@override
Future<BeagleUIElement> fetch(RemoteView route) async {
BeagleUIElement view;
if (_preFetched[route.url] != null) {
view = _preFetched[route.url]!;
_preFetched.remove(route.url);
} else {
view = await fetchView(route);
}
_processPrefetches(view);
return view;
}