We have an open issue that's waiting to be committed to add a method that returns an iterable of all routes; it's not a RouteCollection because there could be an obscene number of routes, so we return a lazy iterator. :-)  It's really only useful for debugging, when you want to get a listing of all routes in the system.  We have it as a separate method in our subinterface of RouteProvider.

Discussion here: https://drupal.org/node/2098197

I'd be happy to normalize the interface with upstream if feasible.