Role management (listing, adding and editing) is being converted to use the entity controllers. Since #1479454: Convert user roles to configurables roles are configuration entities.
The path used to manage roles has been changed to bring it into line with other configuration entities:
D7 admin/people/roles/%role
D8 admin/people/roles/manage/%role
Adding a new role is now on a separate page admin/people/roles/add and is a local task on the roles listing page admin/people/roles. Additionally the ability to add a role within the roles listing has been removed.
Form builder function changes
user_admin_roles() => user_admin_roles_form()
user_admin_role() => uses EntityFormController so user_role_form() can be used to alter the form
Sorting of roles on the listing page has moved to #theme_table so theme_user_admin_roles() has been removed.
Example code
// Form to add new role.
$role = UserRole::create(array());
return entity_get_form($role);
