Handle push resubscribes with no sender info (avoids DCHECK)

chrome/test/data/push_messaging/push_test.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 strict';
 
 // The ResultQueue is a mechanism for passing messages back to the test
 // framework.
 var resultQueue = new ResultQueue();
 
@@ skipping 121 matching lines @@
   }).catch(sendErrorToTest);
 }
 
 function workerSubscribePush() {
   // Send the message to the worker for it to subscribe
   navigator.serviceWorker.controller.postMessage({command: 'workerSubscribe'});
 }
 
 function workerSubscribePushNoKey() {
   // The worker will try to subscribe without providing a key. This should
-  // succeed if the worker was previously subscribed and fail otherwise.
+  // succeed if the worker was previously subscribed with a numeric key
+  // and fail otherwise.
   navigator.serviceWorker.controller.postMessage(
       {command: 'workerSubscribeNoKey'});
 }
 
 function GetP256dh() {
   navigator.serviceWorker.ready.then(function(swRegistration) {
     return swRegistration.pushManager.getSubscription()
         .then(function(subscription) {
           sendResultToTest(btoa(String.fromCharCode.apply(null,
               new Uint8Array(subscription.getKey('p256dh')))));
@@ skipping 65 matching lines @@
   }).catch(sendErrorToTest);
 }
 
 navigator.serviceWorker.addEventListener('message', function(event) {
   var message = JSON.parse(event.data);
   if (message.type == 'push')
     resultQueue.push(message.data);
   else
     sendResultToTest(message.data);
 }, false);