Search: use the same settings object for loading search providers

In recent glib, change notifications don't actually happen unless all
keys have been read, in an effort to reduce unnecessary dbus
traffic for shortlived GSettings object and avoid AddMatch calls.
But we care about changes here, so we need to make sure we're
subscribed, and an easy way to do so is to reuse the same object
to watch for changes and to load the active providers at startup.

https://bugzilla.gnome.org/show_bug.cgi?id=746509

js/ui/search.js

@@ -435,7 +435,7 @@ const SearchResults = new Lang.Class({
             this._unregisterProvider(provider);
         }));
 
-        RemoteSearch.loadRemoteSearchProviders(Lang.bind(this, function(providers) {
+        RemoteSearch.loadRemoteSearchProviders(this._searchSettings, Lang.bind(this, function(providers) {
             providers.forEach(Lang.bind(this, this._registerProvider));
         }));
     },