Add basic browser test for EmbeddedWorker/ServiceWorker

content/test/data/service_worker/worker.js

Index: content/test/data/service_worker/worker.js
diff --git a/chrome/test/data/extensions/platform_apps/ephemeral_apps/messaging_receiver/index.js b/content/test/data/service_worker/worker.js
similarity index 60%
copy from chrome/test/data/extensions/platform_apps/ephemeral_apps/messaging_receiver/index.js
copy to content/test/data/service_worker/worker.js
index dc590d190815d0645476120ece798c9fb5b4db35..b6b90d432e42f131ee402341494d728d5f268d58 100644
--- a/chrome/test/data/extensions/platform_apps/ephemeral_apps/messaging_receiver/index.js
+++ b/content/test/data/service_worker/worker.js
@@ -2,6 +2,5 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-onload = function() {
-  chrome.test.sendMessage('launched');
-};
+// Has no content yet, this just needs to exist for script loading.
+this.oninstalled = function(event) {};