Linux native notifications: Add attribution

ui/message_center/notification.h

Index: ui/message_center/notification.h
diff --git a/ui/message_center/notification.h b/ui/message_center/notification.h
index 8b66c656c927bd5f5fecb5de701dff502e2ab4d8..6aff50c9625e22c7c7b1c85bf0457697b4e66a0d 100644
--- a/ui/message_center/notification.h
+++ b/ui/message_center/notification.h
@@ -129,6 +129,7 @@ class MESSAGE_CENTER_EXPORT Notification {
   // Can be empty if the notification is requested by an extension or
   // Chrome app.
   const GURL& origin_url() const { return origin_url_; }
+  void set_origin_url(const GURL& origin_url) { origin_url_ = origin_url; }
 
   // A display string for the source of the notification.
   const base::string16& display_source() const { return display_source_; }