Change UnionType to IdlType::Union function to include any supported types instead of returning None when there is at least one unsupported type

For example, the constructor in Response.webidl accepts multiple types. However, one of those types is `ReadableStream` which isn't defined yet, and that causes all constructors for Response to be skipped even though the other argument types could be supported.

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

@@ -1,4 +1,12 @@
+extern crate futures;
+extern crate js_sys;
+extern crate wasm_bindgen_futures;
+
+use futures::Future;
+use js_sys::{ArrayBuffer, DataView};
 use wasm_bindgen::prelude::*;
+use wasm_bindgen::JsCast;
+use wasm_bindgen_futures::JsFuture;
 use wasm_bindgen_test::*;
 use web_sys::Response;
 
@@ -8,9 +16,27 @@ extern "C" {
 }
 
 #[wasm_bindgen_test]
-fn test_response() {
+fn test_response_from_js() {
     let response = new_response();
     assert!(!response.ok());
     assert!(!response.redirected());
     assert_eq!(response.status(), 501);
 }
+
+#[wasm_bindgen_test(async)]
+fn test_response_from_bytes() -> impl Future<Item = (), Error = JsValue> {
+    let mut bytes: [u8; 3] = [1, 3, 5];
+    let response = Response::new_with_opt_u8_array(Some(&mut bytes)).unwrap();
+    assert!(response.ok());
+    assert_eq!(response.status(), 200);
+
+    let buf_promise = response.array_buffer().unwrap();
+    JsFuture::from(buf_promise).map(move |buf_val| {
+        assert!(buf_val.is_instance_of::<ArrayBuffer>());
+        let array_buf: ArrayBuffer = buf_val.dyn_into().unwrap();
+        let data_view = DataView::new(&array_buf, 0, bytes.len());
+        for (i, byte) in bytes.iter().enumerate() {
+            assert_eq!(&data_view.get_uint8(i), byte);
+        }
+    })
+}