Push service may be null and must only be used on the UI thread.

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 415d8401b6c747dc26d0c2081199abcfb8cfdf1f..d28786fa9510db35adf0626ee1ffc30a36c12c67 100644
--- a/content/browser/push_messaging/push_messaging_message_filter.cc
+++ b/content/browser/push_messaging/push_messaging_message_filter.cc
@@ -206,6 +206,11 @@ void PushMessagingMessageFilter::DoPermissionStatusRequest(
     int render_frame_id,
     int callback_id) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (!service()) {
+    Send(new PushMessagingMsg_PermissionStatusFailure(render_frame_id,
+                                                      callback_id));
+    return;
+  }
   blink::WebPushPermissionStatus permission_value =
       service()->GetPermissionStatus(
           requesting_origin, render_process_id_, render_frame_id);
@@ -218,6 +223,10 @@ void PushMessagingMessageFilter::GetPermissionStatusOnUI(
     const GURL& requesting_origin,
     int request_id) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (!service()) {
+    Send(new PushMessagingMsg_GetPermissionStatusError(request_id));
+    return;
+  }
   GURL embedding_origin = requesting_origin;
   blink::WebPushPermissionStatus permission_status =
       service()->GetPermissionStatus(requesting_origin, embedding_origin);
@@ -264,6 +273,7 @@ void PushMessagingMessageFilter::SendRegisterSuccess(
 }
 
 PushMessagingService* PushMessagingMessageFilter::service() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
   if (!service_) {
     RenderProcessHost* process_host =
         RenderProcessHost::FromID(render_process_id_);