[Background Fetch] Fix match() crash.

background-fetch/fetch.https.window.js

@@ -282,3 +282,41 @@ backgroundFetchTest(async (test, backgroundFetch) => {
   assert_equals(nullResponse, null);
 
 }, 'Fetches with mixed content should fail.');
+
+backgroundFetchTest(async (test, backgroundFetch) => {
+  const registrationId = 'matchexistingrequest';
+  const registration =
+    await backgroundFetch.fetch(registrationId, 'resources/feature-name.txt');
+
+  assert_equals(registration.id, registrationId);
+
+  const {type, eventRegistration, results} = await getMessageFromServiceWorker();
+  assert_equals('backgroundfetchsuccess', type);
+  assert_equals(results.length, 1);
+
+  assert_equals(eventRegistration.id, registration.id);
+  assert_equals(eventRegistration.result, 'success');
+  assert_equals(eventRegistration.failureReason, '');
+
+  assert_true(results[0].url.includes('resources/feature-name.txt'));
+  assert_equals(results[0].status, 200);
+  assert_equals(results[0].text, 'Background Fetch');
+
+}, 'Matching to a single request should work');
+
+backgroundFetchTest(async (test, backgroundFetch) => {
+  const registrationId = 'matchmissingrequest';
+  const registration =
+    await backgroundFetch.fetch(registrationId, 'resources/feature-name.txt');
+
+  assert_equals(registration.id, registrationId);
+
+  const {type, eventRegistration, results} = await getMessageFromServiceWorker();
+  assert_equals('backgroundfetchsuccess', type);
+  assert_equals(results.length, 0);
+
+  assert_equals(eventRegistration.id, registration.id);
+  assert_equals(eventRegistration.result, 'success');
+  assert_equals(eventRegistration.failureReason, '');
+
+}, 'Matching to a non-existing request should work');

background-fetch/service_workers/sw.js

@@ -13,10 +13,33 @@ async function getFetchResult(record) {
 }
 
 function handleBackgroundFetchEvent(event) {
+  let matchFunction = null;
+  switch (event.registration.id) {
+    case 'matchexistingrequest':
+      matchFunction = event.registration.match.bind(
+          event.registration, '/background-fetch/resources/feature-name.txt');
+      break;
+    case 'matchmissingrequest':
+      matchFunction = event.registration.match.bind(
+          event.registration, '/background-fetch/resources/missing.txt');
+      break;
+    default:
+      matchFunction = event.registration.matchAll.bind(event.registration);
+      break;
+  }
+
   event.waitUntil(
-    event.registration.matchAll()
+    matchFunction()
+      // Format `match(All)?` function results.
+      .then(records => {
+        if (!records) return [];  // Nothing was matched.
+        if (!records.map) return [records];  // One entry was returned.
+        return records;  // Already in a list.
+      })
+      // Extract responses.
       .then(records =>
             Promise.all(records.map(record => getFetchResult(record))))
+      // Clone registration and send message.
       .then(results => {
         const registrationCopy = cloneRegistration(event.registration);
         sendMessageToDocument(