Update web-sys test to only test compilation

Author: alexcrichton

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

@@ -7,7 +7,6 @@ extern crate wasm_bindgen_futures;
 extern crate wasm_bindgen_test;
 extern crate web_sys;
 
-use wasm_bindgen::{JsValue, JsCast};
 use wasm_bindgen_test::*;
 
 wasm_bindgen_test_configure!(run_in_browser);
@@ -60,8 +59,10 @@ pub mod indexeddb;
 
 #[wasm_bindgen_test]
 fn deref_works() {
-    let x = JsValue::from(3);
-    let x = x.unchecked_into::<web_sys::XmlHttpRequestUpload>();
-    let y: &web_sys::XmlHttpRequestEventTarget = &x;
-    drop(y);
+    fn _check(a: &web_sys::XmlHttpRequestUpload) {
+        let _x: &web_sys::XmlHttpRequestEventTarget = a;
+        let _x: &web_sys::EventTarget = a;
+        let _x: &js_sys::Object = a;
+        let _x: &wasm_bindgen::JsValue = a;
+    }
 }