Fix flaky SW registration in PushMessaging/BudgetManager browser tests

chrome/test/data/push_messaging/service_worker.js

 // Copyright 2014 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.
 
 // Use an absolute path since this could be loaded from a different scope,
 // which would affect the scope of the importScripts call here.
 self.importScripts('/push_messaging/push_constants.js');
 
+// Don't wait for clients of old SW to close before activating.
+self.addEventListener('install', () => skipWaiting());
+
 // The "onpush" event currently understands two values as message payload
 // data coming from the test. Any other input is passed through to the
 // document unchanged.
 //
 // "shownotification" - Display a Web Notification with event.waitUntil().
 // "shownotification-without-waituntil"
 //     - Display a Web Notification without using event.waitUntil().
 this.onpush = function(event) {
   if (event.data === null) {
     sendMessageToClients('push', '[NULL]');
@@ skipping 54 matching lines @@
     'data': data
   });
   clients.matchAll().then(function(clients) {
     clients.forEach(function(client) {
       client.postMessage(message);
     });
   }, function(error) {
     console.log(error);
   });
 }