[gnome-shell] background: Don't silently fizzle out when removing bad content from the cache

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

commit 7249b118993474b7e6358f82e872d7735154e796
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Tue Dec 3 17:54:02 2013 -0500

    background: Don't silently fizzle out when removing bad content from the cache
    
    If the background is already removed, or we're trying to remove bad content,
    this is probably a bug in content accounting, so let us crash so we can fix
    the bugs.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=719803

 js/ui/background.js |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/js/ui/background.js b/js/ui/background.js
index 885e96b..a56a0af 100644
--- a/js/ui/background.js
+++ b/js/ui/background.js
@@ -113,9 +113,9 @@ const BackgroundCache = new Lang.Class({
 
     _removeContent: function(contentList, content) {
         let index = contentList.indexOf(content);
-
-        if (index >= 0)
-            contentList.splice(index, 1);
+        if (index < 0)
+            throw new Error("Trying to remove invalid content: " + content);
+        contentList.splice(index, 1);
     },
 
     removePatternContent: function(content) {