Extension SW - add test for ServiceWorkerRegistration.sync.

chrome/test/data/extensions/api_test/service_worker/sync/sw.js

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+var port = null;
+this.onsync = function(e) {
+  if (port) {
+    e.waitUntil(new Promise(function(resolve) {

[Devlin, 2015/11/16 18:12:41]

Maybe I'm missing something - when does this resolve?

[lazyboy, 2015/11/16 19:30:16]

It never did. Fixed.

+      // Add a small delay to respond so we can exercise and test the
+      // offline->online transition.

[Devlin, 2015/11/16 18:12:41]

"small delays" usually correspond to flakiness.  Is there a reason we need it,
since we're not (in theory) executing any of this code until after the web
contents is offline?

[lazyboy, 2015/11/16 19:30:16]

We don't really need it, but this might catch some corner case
later on.
I've changed the comment a bit.

+      setTimeout(function() {
+        port.postMessage('SYNC: ' + e.registration.tag);
+      }, 5);
+    }));
+  }
+};
+
+this.onmessage = function(e) {
+  port = e.ports[0];
+};