Method visit

1472-design-browser-history.rs:15–19

(&mut self, url: String)

    }

    fn visit(&mut self, url: String) {
        self.his.truncate(self.idx + 1);
        self.his.push(url.clone());
        self.idx += 1;
    }

    fn back(&mut self, steps: i32) -> String {
        let steps = steps as usize;