[gnome-shell] background: don't use raise_top() since it's costly

[Ray Strode <halfline src gnome org>]

commit 020128b9ca801f87f158e921f14f0ae585334008
Author: Ray Strode <rstrode redhat com>
Date:   Tue Mar 5 15:39:29 2013 -0500

    background: don't use raise_top() since it's costly
    
    We currently resync the stacking order of the two key frames
    every iteration of the animation.  This is costly and unnecessary.
    
    This commit ensures they're stacked properly up front and doesn't
    touch them after that.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=694993

 js/ui/background.js |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)
---
diff --git a/js/ui/background.js b/js/ui/background.js
index 74e398e..6d6089b 100644
--- a/js/ui/background.js
+++ b/js/ui/background.js
@@ -356,7 +356,7 @@ const Background = new Lang.Class({
 
         let actor = new Meta.BackgroundActor();
         actor.content = content;
-        this.actor.add_child(actor);
+        this.actor.insert_child_at_index(actor, index);
 
         this._images[index] = actor;
         this._watchCacheFile(filename);
@@ -372,10 +372,8 @@ const Background = new Lang.Class({
     },
 
     _updateAnimationProgress: function() {
-        if (this._images[1]) {
-            this._images[1].raise_top();
+        if (this._images[1])
             this._images[1].opacity = this._animation.transitionProgress * 255;
-        }
 
         this._queueAnimationUpdate();
     },