[fetch-later] Implement basic FetchLater method

Add the basic algorithm steps from [FetchLater method][1], which mostly includes:
- Checks abort signal
- Checks request URL
- Adds extra abort steps

Subsequent CL will implement the missing steps:
- Add quota checking steps from [Deferred fetch][2]
  https://crrev.com/c/4835437
- Add backgroundTimeout https://crrev.com/c/4803283
- throw TypeError for ReadableStream (TBD from spec discussion)

[1]: https://whatpr.org/fetch/1647/53e4c3d...71fd383.html#fetch-later-method
[2]: https://whatpr.org/fetch/1647/53e4c3d...71fd383.html#deferred-fetching

Bug: 1465781
Change-Id: Ifc1a401ae000aa695dbdb3dc375557fac972b519
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4820528
Commit-Queue: Ming-Ying Chung <[email protected]>
Reviewed-by: Nidhi Jaju <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1191973}

fetch/fetch-later/basic.tentative.https.window.js

@@ -7,7 +7,29 @@ test(() => {
   assert_throws_js(TypeError, () => fetchLater());
 }, `fetchLater() cannot be called without request.`);
 
+test(() => {
+  assert_throws_js(TypeError, () => fetchLater('http://www.google.com'));
+  assert_throws_js(TypeError, () => fetchLater('file://tmp'));
+  assert_throws_js(TypeError, () => fetchLater('ssh://example.com'));
+  assert_throws_js(TypeError, () => fetchLater('wss://example.com'));
+  assert_throws_js(TypeError, () => fetchLater('about:blank'));
+  assert_throws_js(TypeError, () => fetchLater(`javascript:alert('');`));
+}, `fetchLater() throws TypeError on non-HTTPS URL.`);
+
 test(() => {
   const result = fetchLater('/');
-  assert_false(result.sent);
+  assert_false(result.activated);
 }, `fetchLater()'s return tells the deferred request is not yet sent.`);
+
+test(() => {
+  const result = fetchLater('/');
+  assert_throws_js(TypeError, () => result.activated = true);
+}, `fetchLater() throws TypeError when mutating its returned state.`);
+
+test(() => {
+  const controller = new AbortController();
+  // Immediately aborts the controller.
+  controller.abort();
+  assert_throws_dom(
+      'AbortError', () => fetchLater('/', {signal: controller.signal}));
+}, `fetchLater() throws AbortError when its initial abort signal is aborted.`);

fetch/fetch-later/send-on-discard.tentative.https.window.js

@@ -0,0 +1,46 @@
+// META: script=/resources/testharness.js
+// META: script=/resources/testharnessreport.js
+// META: script=/common/utils.js
+// META: script=/pending-beacon/resources/pending_beacon-helper.js
+
+'use strict';
+
+parallelPromiseTest(async t => {
+  const uuid = token();
+  const url = generateSetBeaconURL(uuid);
+  const numPerMethod = 20;
+  const total = numPerMethod * 2;
+
+  // Loads an iframe that creates `numPerMethod` GET & POST fetchLater requests.
+  const iframe = await loadScriptAsIframe(`
+    const url = "${url}";
+    for (let i = 0; i < ${numPerMethod}; i++) {
+      fetchLater(url);
+      fetchLater(url, {method: 'POST'});
+    }
+  `);
+  // Delete the iframe to trigger deferred request sending.
+  document.body.removeChild(iframe);
+
+  // The iframe should have sent all requests.
+  await expectBeacon(uuid, {count: total});
+}, 'A discarded document sends all its fetchLater requests.');
+
+parallelPromiseTest(async t => {
+  const uuid = token();
+  const url = generateSetBeaconURL(uuid);
+
+  // Loads an iframe that creates 2 fetchLater requests. One of them is aborted.
+  const iframe = await loadScriptAsIframe(`
+    const url = "${url}";
+    const controller = new AbortController();
+    fetchLater(url, {signal: controller.signal});
+    fetchLater(url, {method: 'POST'});
+    controller.abort();
+  `);
+  // Delete the iframe to trigger deferred request sending.
+  document.body.removeChild(iframe);
+
+  // The iframe should not send the aborted request.
+  await expectBeacon(uuid, {count: 1});
+}, 'A discarded document does not send an already aborted fetchLater request.');