ShellRecorder: update to use MetaCursorTracker

Replace more direct XFixes usage with a the appropriate abstraction
API from mutter, which is guaranteed to work in wayland too.

It doesn't yet replace pointer position tracking, although probably
it should.
Also, because now we're using Mutter API, we lose the standalone
test case.

https://bugzilla.gnome.org/show_bug.cgi?id=705911

js/ui/screencast.js

@@ -52,7 +52,8 @@ const ScreencastService = new Lang.Class({
     _ensureRecorderForSender: function(sender) {
         let recorder = this._recorders.get(sender);
         if (!recorder) {
-            recorder = new Shell.Recorder({ stage: global.stage });
+            recorder = new Shell.Recorder({ stage: global.stage,
+                                            screen: global.screen });
             recorder._watchNameId =
                 Gio.bus_watch_name(Gio.BusType.SESSION, sender, 0, null,
                                    Lang.bind(this, this._onNameVanished));