DOM: test listener invocation order

For whatwg/dom#686.

dom/events/Event-dispatch-listener-order.window.js

@@ -0,0 +1,20 @@
+test(t => {
+  const hostParent = document.createElement("section"),
+        host = hostParent.appendChild(document.createElement("div")),
+        shadowRoot = host.attachShadow({ mode: "closed" }),
+        targetParent = shadowRoot.appendChild(document.createElement("p")),
+        target = targetParent.appendChild(document.createElement("span")),
+        path = [hostParent, host, shadowRoot, targetParent, target],
+        expected = [],
+        result = [];
+  path.forEach((node, index) => {
+    expected.splice(index, 0, "capturing " + node.nodeName);
+    expected.splice(index + 1, 0, "bubbling " + node.nodeName);
+  });
+  path.forEach(node => {
+    node.addEventListener("test", () => { result.push("bubbling " + node.nodeName) });
+    node.addEventListener("test", () => { result.push("capturing " + node.nodeName) }, true);
+  });
+  target.dispatchEvent(new CustomEvent('test', { detail: {}, bubbles: true, composed: true }));
+  assert_array_equals(result, expected);
+});