WorkerLocation: ensure IDNA origin is in ASCII

For whatwg/html#2568.

workers/WorkerLocation-origin.sub.window.js

@@ -0,0 +1,11 @@
+async_test(t => {
+  const frame = document.createElement("iframe"),
+        asciiOrigin = location.protocol + "//{{domains[天気の良い日]}}:" + location.port,
+        path = new URL("support/WorkerLocation-origin.html", location).pathname;
+  frame.src = asciiOrigin + path;
+  self.onmessage = t.step_func_done(e => {
+    assert_equals(e.data.origin, asciiOrigin);
+  });
+  document.body.appendChild(frame);
+  t.add_cleanup(() => frame.remove());
+}, "workerLocation.origin must use ASCII code points");

workers/support/WorkerLocation-origin.html

@@ -0,0 +1,6 @@
+<script>
+const w = new Worker("./WorkerLocation.js");
+w.onmessage = e => {
+  parent.postMessage(e.data, "*");
+}
+</script>

workers/support/WorkerLocation.js

@@ -1,6 +1,7 @@
 var obj = new Object();
 obj.location = location.toString();
 obj.href     = location.href;
+obj.origin   = location.origin;
 obj.protocol = location.protocol;
 obj.host     = location.host;
 obj.hostname = location.hostname;