Revert of Revert of ServiceWorker: Remove Clients.getAll()

LayoutTests/http/tests/serviceworker/chromium/resources/sw-test-helpers.js

 // Test helper that is meant as a mini test framework to be used from a service
 // worker that runs some tests and send results back to its client.
 //
 // A simple usage of this framework would consist of calling initialize() to
 // setup then runNextTestOrQuit() in order to start running the methods defined
 // by TESTS. Then, tests can start sending messages back to the client using
 // postMessage().
 //
 // Example:
 // var TESTS = [
 //     function simpleTest() {
 //         self.postMessage('you will receive this first');
 //     },
 //     function secondTest() {
 //         self.postMessage('secondTest done!');
 //         runNextTestOrQuit();
 //     }
 // ];
 //
 // initialize().runNextTestOrQuit();
 //
 // In addition, there is a helper method meant to synthesized notificationclick
 // events sent to a service worker, see synthesizeNotificationClick.
 
 var client = null;
 var currentTest = -1;
 
 self.initialize = function() {
-    return self.clients.getAll().then(function(clients) {
+    return self.clients.matchAll().then(function(clients) {
         client = clients[0];
     });
 }
 
 self.postMessage = function(msg) {
     client.postMessage(msg);
 }
 
 // Run the next test in TESTS if any. Otherwise sends a 'quit' message. and
 // stops.
@@ skipping 23 matching lines @@
             resolve(e);
             e.notification.close();
             self.removeEventListener('notificationclick', handler);
         };
 
         self.addEventListener('notificationclick', handler);
     });
 
     return promise;
 }