Add unit tests for even more 'web-sys' bindings

That list includes:
 * HtmlMenuElement
 * HtmlMenuItemElement
 * HtmlMetaElement
 * HtmlMeterElement

crates/web-sys/tests/wasm/meter_element.rs

@@ -0,0 +1,33 @@
+use wasm_bindgen_test::*;
+use wasm_bindgen::prelude::*;
+use web_sys::HtmlMeterElement;
+
+#[wasm_bindgen(module = "./tests/wasm/element.js")]
+extern {
+    fn new_meter() -> HtmlMeterElement;
+}
+
+#[wasm_bindgen_test]
+fn test_meter_element() {
+    let meter = new_meter();
+
+    meter.set_min(-5.);
+    assert_eq!(meter.min(), -5., "Meter should have the min value we gave it.");
+
+    meter.set_max(5.);
+    assert_eq!(meter.max(), 5., "Meter should have the max value we gave it.");
+
+    meter.set_value(2.);
+    assert_eq!(meter.value(), 2., "Meter should have the value we gave it.");
+
+    meter.set_low(-1.);
+    assert_eq!(meter.low(), -1., "Meter should have the low value we gave it.");
+
+    meter.set_high(1.);
+    assert_eq!(meter.high(), 1., "Meter should have the high value we gave it.");
+
+    meter.set_optimum(3.);
+    assert_eq!(meter.optimum(), 3., "Meter should have the optimum value we gave it.");
+
+    assert!(meter.labels().length() == 0, "Our meter shouldn't have any labels associated with it.");
+}