Make Instance actually stand alone.

channel.py

@@ -33,17 +33,23 @@ class OnChannelConnect(webapp2.RequestHandler):
 
 
 class OnChannelDisconnect(webapp2.RequestHandler):
+  @staticmethod
+  @db.transactional()
+  def DeleteInstance(instance_id):
+    instance = models.Instance.FromID(instance_id)
+    ret = instance.key()
+    instance.delete()
+    return ret
+
   @utils.local_namespace
   def post(self):
     instance_id = self.request.get('from')
-    instance = models.Instance.FromID(instance_id)
+    instance_key = self.DeleteInstance(instance_id)
 
-    subscriptions = models.Subscription.all().filter('instance =', instance)
+    subscriptions = models.Subscription.all().filter('instance =', instance_key)
     for subscription in subscriptions:
       subscription.delete()
 
-    instance.delete()
-
 
 app = webapp2.WSGIApplication([
   ('/_ah/channel/connected/', OnChannelConnect),