Handle push resubscribes with no sender info (avoids DCHECK)

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());
@@ skipping 33 matching lines @@
     sendMessageToClients('push', String(ex));
   }));
 };
 
 self.addEventListener('message', function handler (event) {
   let pushSubscriptionOptions = {
       userVisibleOnly: true
   };
   if (event.data.command == 'workerSubscribe') {
     pushSubscriptionOptions.applicationServerKey = kApplicationServerKey.buffer;
+  } else if (event.data.command == 'workerSubscribePushWithNumber') {

[harkness, 2016/11/02 18:48:12]

nit NumericKey?

[awdf, 2016/11/03 14:10:11]

Oops, this actually isn't called, (since it's one of those 'only support for
simplicity' cases, I didn't write explicit tests for it in the end). Removed.

[awdf, 2016/11/07 16:54:30]

Reinstated. Discussing with John we figured it's not such a bad idea to have
explicit tests for those yellow cases after all, in order to notice if something
changes, so long as there's a comment saying it's not ideal behaviour.

+    pushSubscriptionOptions.applicationServerKey =
+        new TextEncoder().encode('1234567890');
   } else if (event.data.command == 'workerSubscribeNoKey') {
     // Nothing to set up
   } else {
     sendMessageToClients('message', 'error - unknown message request');
     return;
   }
 
   self.registration.pushManager.subscribe(pushSubscriptionOptions)
       .then(function(subscription) {
         sendMessageToClients('message', subscription.endpoint);
@@ skipping 12 matching lines @@
     'data': data
   });
   clients.matchAll().then(function(clients) {
     clients.forEach(function(client) {
       client.postMessage(message);
     });
   }, function(error) {
     console.log(error);
   });
 }