Reject push registrations when no sender Id has been provided.

content/public/common/push_messaging_status.cc

Index: content/public/common/push_messaging_status.cc
diff --git a/content/public/common/push_messaging_status.cc b/content/public/common/push_messaging_status.cc
index 7c476408d6ea8b6c6949e01051198f8703973f81..d3b3d1b9dc51f2b95da738141b17277caf961aa6 100644
--- a/content/public/common/push_messaging_status.cc
+++ b/content/public/common/push_messaging_status.cc
@@ -27,6 +27,9 @@ const char* PushRegistrationStatusToString(PushRegistrationStatus status) {
 
     case PUSH_REGISTRATION_STATUS_SERVICE_ERROR:
       return "Registration failed - push service error";
+
+    case PUSH_REGISTRATION_STATUS_NO_SENDER_ID:
+      return "Registration failed - no sender id provided";
   }
   NOTREACHED();
   return "";