Handle push resubscribes with no sender info (avoids DCHECK)

chrome/test/data/push_messaging/push_test.js

Index: chrome/test/data/push_messaging/push_test.js
diff --git a/chrome/test/data/push_messaging/push_test.js b/chrome/test/data/push_messaging/push_test.js
index 4c7fb761c3b01e57f6f801471301a57652d8dc08..f0130ef9332982d61adef153fec850ee7548c0c1 100644
--- a/chrome/test/data/push_messaging/push_test.js
+++ b/chrome/test/data/push_messaging/push_test.js
@@ -139,7 +139,8 @@ function workerSubscribePush() {
 
 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'});
 }