[Background Fetch] Throw DOMException for responseReady on abort.

According to the spec, responseReady in BackgroundFetchRecord should
throw an AbortError DOMException if the fetch was abandoned.

https://wicg.github.io/background-fetch/#create-record-objects (2.4.3)

Change-Id: Ieadf278acd061e05b8822014d0934f050fcac702
Reviewed-on: https://chromium-review.googlesource.com/c/1283692
Commit-Queue: Rayan Kanso <rayankans@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600769}

background-fetch/abort.https.window.js

@@ -59,4 +59,16 @@ backgroundFetchTest(async (test, backgroundFetch) => {
     };
   });
 
-}, 'Calling BackgroundFetchRegistration.abort sets the correct fields and responses are still available');
+}, 'Calling BackgroundFetchRegistration.abort sets the correct fields and responses are still available');
+
+backgroundFetchTest(async (test, backgroundFetch) => {
+  const registration = await backgroundFetch.fetch(
+      uniqueId(), '/serviceworker/resources/slow-response.php');
+  assert_true(await registration.abort());
+
+  const {results} = await getMessageFromServiceWorker();
+  assert_equals(results.length, 1);
+  assert_false(results[0].response);
+  assert_equals(results[0].name, 'AbortError');
+
+}, 'An aborted fetch throws a DOM exception when accessing an incomplete record', 'sw-abort.js');

background-fetch/service_workers/sw-abort.js

@@ -0,0 +1,23 @@
+importScripts('sw-helpers.js');
+
+async function getFetchResult(record) {
+  try {
+    await record.responseReady;
+  } catch (e) {
+    return {
+      response: false,
+      name: e.name,
+    };
+  }
+
+  return {
+    response: true,
+  };
+}
+self.addEventListener('backgroundfetchabort', event => {
+  event.waitUntil(
+    event.registration.matchAll()
+      .then(records =>
+            Promise.all(records.map(record => getFetchResult(record))))
+      .then(results => sendMessageToDocument({results})));
+});