Function keys_rev

cranelift/entity/src/primary.rs:485–495

()

    #[test]
    fn keys_rev() {
        let mut m: PrimaryMap<E, usize> = PrimaryMap::new();
        m.push(12);
        m.push(33);

        let mut i = 2;
        for key in m.keys().rev() {
            i -= 1;
            assert_eq!(key.index(), i);
        }
    }

    #[test]
    fn values() {