Add button element tests for web-sys. (#577)

crates/web-sys/tests/all/head_element.rs

@@ -0,0 +1,33 @@
+use super::websys_project;
+
+#[test]
+fn head_element() {
+    websys_project()
+        .file(
+            "src/lib.rs",
+            r#"
+                #![feature(use_extern_macros, wasm_custom_section)]
+                extern crate wasm_bindgen;
+                use wasm_bindgen::prelude::*;
+                extern crate web_sys;
+
+                #[wasm_bindgen]
+                pub fn test_head_element(_element: &web_sys::HtmlHeadElement) {
+                    assert!(true, "Head doesn't have an interface");
+                }
+            "#,
+        )
+        .file(
+            "test.js",
+            r#"
+                import * as assert from "assert";
+                import * as wasm from "./out";
+
+                export function test() {
+                    let head = document.createElement("head");
+                    wasm.test_head_element(head);
+                }
+            "#,
+        )
+        .test();
+}