ServiceWorker: Implement ServiceWorkerRegistration.update() (3)

LayoutTests/http/tests/serviceworker/ServiceWorkerGlobalScope/resources/update-worker.php

+<?php
+// Force the browser to cache this script. update() should always bypass this
+// cache and fetch a new version.
+header('Cache-Control: max-age=86400');
+
+// Return a different script for each access.
+header('Content-Type:application/javascript');
+echo '// ' . microtime();
+?>
+
+importScripts('../../resources/test-helpers.js');
+importScripts('../../resources/worker-testharness.js');
+
+var events_seen = [];
+
+self.registration.addEventListener('updatefound', function() {
+    events_seen.push('updatefound');
+  });
+
+self.addEventListener('activate', function(e) {
+    events_seen.push('activate');
+  });
+
+self.addEventListener('fetch', function(e) {
+    events_seen.push('fetch');
+    e.respondWith(new Response(events_seen));
+  });
+
+self.addEventListener('message', function(e) {
+    events_seen.push('message');
+    self.registration.update();
+  });
+
+// update() during the script evaluation should be ignored.
+self.registration.update();