Add a benchmark for tokenization of a large stylesheet.

Author: emilio

src/big-stylesheet.css

@@ -601,6 +601,24 @@ fn unquoted_url(b: &mut Bencher) {
     })
 }
 
+#[cfg(feature = "bench")]
+const BIG_STYLESHEET: &'static str = include_str!("big-stylesheet.css");
+
+#[cfg(feature = "bench")]
+#[bench]
+fn big_stylesheet(b: &mut Bencher) {
+    b.iter(|| {
+        let mut input = Parser::new(BIG_STYLESHEET);
+        input.look_for_var_functions();
+
+        let mut last_token = None;
+        while let Ok(tok) = input.next() {
+            last_token = Some(test::black_box(tok));
+        }
+        last_token
+    })
+}
+
 struct JsonParser;
 
 #[test]