[Background Sync] Update idlharness test

to add a list of expected objects.

Bug: 996664
Change-Id: I8b13a849a82687ae2d2c9f41856569391c02a35d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1912206
Commit-Queue: Mike West <mkwst@chromium.org>
Auto-Submit: Mugdha Lakhani <nator@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715387}

third_party/blink/web_tests/external/wpt/BackgroundSync/idlharness.https.any.js

@@ -9,6 +9,16 @@ idl_test(
   ['BackgroundSync'],
   ['service-workers', 'html', 'dom'],
   idlArray => {
-    // TODO: Objects
+    const isServiceWorker = location.pathname.includes('.serviceworker.');
+    if (isServiceWorker) {
+      idl_array.add_objects({
+        ServiceWorkerGlobalScope: ['self', 'onsync', 'onperiodicsync'],
+        ServiceWorkerRegistration: ['registration'],
+        SyncManager: ['registration.sync'],
+        PeriodicSyncManager: ['registration.periodicSync'],
+        SyncEevnt: ['new SyncEvent("tag", "lastChance")'],
+        PeriodicSyncEevnt: ['new PeriodicSyncEvent("tag")'],
+      });
   }
+}
 );