[gnome-shell] messageTray: Make Tweener shut up about normal properties

[Jasper St. Pierre <jstpierre src gnome org>]

commit 4e7000988d3a8374c1587383284910a2c531ec77
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Fri Feb 20 18:11:58 2015 -0800

    messageTray: Make Tweener shut up about normal properties
    
    Tweener needs an initial value to tween from, otherwise it won't
    work, so give it something it can use.

 js/ui/messageTray.js |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/js/ui/messageTray.js b/js/ui/messageTray.js
index 9e9f7af..345dede 100644
--- a/js/ui/messageTray.js
+++ b/js/ui/messageTray.js
@@ -1902,6 +1902,7 @@ const MessageTray = new Lang.Class({
 
         this.actor.add_actor(this._banner.actor);
 
+        this.actor._opacity = 0;
         this.actor.opacity = 0;
         this.actor.y = -this._banner.actor.height;
         this.actor.show();