Remove support for the "gcm_user_visible_only" manifest key.

content/browser/push_messaging/push_messaging_message_filter.cc

Index: content/browser/push_messaging/push_messaging_message_filter.cc
diff --git a/content/browser/push_messaging/push_messaging_message_filter.cc b/content/browser/push_messaging/push_messaging_message_filter.cc
index e6a869b09ab36fbe5890ae77afc32eca15e20f54..836d83fbe121faa4631dfe3bcf6d131a0ac8eef6 100644
--- a/content/browser/push_messaging/push_messaging_message_filter.cc
+++ b/content/browser/push_messaging/push_messaging_message_filter.cc
@@ -217,7 +217,6 @@ void PushMessagingMessageFilter::OnSubscribeFromDocument(
     int64_t service_worker_registration_id) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   // TODO(mvanouwerkerk): Validate arguments?
-  // TODO(peter): Persist |user_visible| in Service Worker storage.
   RegisterData data;
   data.request_id = request_id;
   data.service_worker_registration_id = service_worker_registration_id;