test: pull html/webappapis/microtask-queuing WPT

With the command:

```
git node wpt html/webappapis/microtask-queuing
```

PR-URL: #25616
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gus Caplan <me@gus.host>

test/fixtures/wpt/README.md

@@ -15,6 +15,7 @@ Last update:
 - url: https://github.com/web-platform-tests/wpt/tree/75b0f336c5/url
 - resources: https://github.com/web-platform-tests/wpt/tree/679a364421/resources
 - interfaces: https://github.com/web-platform-tests/wpt/tree/712c9f275e/interfaces
+- html/webappapis/microtask-queuing: https://github.com/web-platform-tests/wpt/tree/0c3bed38df/html/webappapis/microtask-queuing
 
 [Web Platform Tests]: https://github.com/web-platform-tests/wpt
 [`git node wpt`]: https://github.com/nodejs/node-core-utils/blob/master/docs/git-node.md#git-node-wpt

test/fixtures/wpt/html/webappapis/microtask-queuing/queue-microtask-exceptions.any.js

@@ -0,0 +1,15 @@
+// META: global=window,worker
+"use strict";
+
+setup({
+  allow_uncaught_exception: true
+});
+
+async_test(t => {
+  const error = new Error("boo");
+  self.addEventListener("error", t.step_func_done(ev => {
+    assert_equals(ev.error, error);
+  }));
+
+  queueMicrotask(() => { throw error; });
+}, "It rethrows exceptions");

test/fixtures/wpt/html/webappapis/microtask-queuing/queue-microtask.any.js

@@ -0,0 +1,39 @@
+// META: global=window,worker
+"use strict";
+
+test(() => {
+  assert_equals(typeof queueMicrotask, "function");
+}, "It exists and is a function");
+
+test(() => {
+  assert_throws(new TypeError(), () => queueMicrotask(), "no argument");
+  assert_throws(new TypeError(), () => queueMicrotask(undefined), "undefined");
+  assert_throws(new TypeError(), () => queueMicrotask(null), "null");
+  assert_throws(new TypeError(), () => queueMicrotask(0), "0");
+  assert_throws(new TypeError(), () => queueMicrotask({ handleEvent() { } }), "an event handler object");
+  assert_throws(new TypeError(), () => queueMicrotask("window.x = 5;"), "a string");
+}, "It throws when given non-functions");
+
+async_test(t => {
+  let called = false;
+  queueMicrotask(t.step_func_done(() => {
+    called = true;
+  }));
+  assert_false(called);
+}, "It calls the callback asynchronously");
+
+async_test(t => {
+  queueMicrotask(t.step_func_done(function () { // note: intentionally not an arrow function
+    assert_array_equals(arguments, []);
+  }), "x", "y");
+}, "It does not pass any arguments");
+
+async_test(t => {
+  const happenings = [];
+  Promise.resolve().then(() => happenings.push("a"));
+  queueMicrotask(() => happenings.push("b"));
+  Promise.reject().catch(() => happenings.push("c"));
+  queueMicrotask(t.step_func_done(() => {
+    assert_array_equals(happenings, ["a", "b", "c"]);
+  }));
+}, "It interleaves with promises as expected");

test/fixtures/wpt/html/webappapis/microtask-queuing/queue-microtask.window.js

@@ -0,0 +1,45 @@
+"use strict";
+
+// This does not work as you expect because mutation observer compound microtasks are confusing.
+// Basically you can only use it once per test.
+function queueMicrotaskViaMO(cb) {
+  const observer = new MutationObserver(cb);
+  const node = document.createTextNode("");
+  observer.observe(node, { characterData: true });
+  node.data = "foo";
+}
+
+// Need to use promise_test to get sequential ordering; otherwise the global mutation observer
+// compound microtask business screws us over.
+
+promise_test(() => {
+  return new Promise(resolve => {
+    const happenings = [];
+
+    queueMicrotaskViaMO(() => happenings.push("x"));
+    queueMicrotask(() => happenings.push("a"));
+
+    queueMicrotask(() => {
+      assert_array_equals(happenings, ["x", "a"]);
+      resolve();
+    });
+  });
+}, "It interleaves with MutationObservers as expected");
+
+promise_test(() => {
+  return new Promise(resolve => {
+    const happenings = [];
+
+    queueMicrotask(() => happenings.push("a"));
+    Promise.reject().catch(() => happenings.push("x"));
+    queueMicrotaskViaMO(() => happenings.push(1));
+    Promise.resolve().then(() => happenings.push("y"));
+    queueMicrotask(() => happenings.push("b"));
+    queueMicrotask(() => happenings.push("c"));
+
+    queueMicrotask(() => {
+      assert_array_equals(happenings, ["a", "x", 1, "y", "b", "c"]);
+      resolve();
+    });
+  });
+}, "It interleaves with MutationObservers and promises together as expected");

test/fixtures/wpt/versions.json

@@ -18,5 +18,9 @@
   "interfaces": {
     "commit": "712c9f275e83997884749dbcaa503f12c0ff5bba",
     "path": "interfaces"
+  },
+  "html/webappapis/microtask-queuing": {
+    "commit": "0c3bed38df6d9dcd1441873728fb5c1bb59c92df",
+    "path": "html/webappapis/microtask-queuing"
   }
 }