overview: Restore previous workspace switcher policy

We used to keep the workspace switcher slid out when the user made use
of workspaces. This was changed in commit 2d849759 to give more space
to window previews, but it turned out to make the switcher quite a lot
more difficult to interact with (rather than only being a question of
discoverability). So go back to the previous behavior.

!161

js/ui/overviewControls.js

@@ -253,13 +253,23 @@ var ThumbnailsSlider = new Lang.Class({
         this.actor.add_actor(this._thumbnailsBox.actor);
 
         Main.layoutManager.connect('monitors-changed', this._updateSlide.bind(this));
+        global.workspace_manager.connect('active-workspace-changed',
+                                         this._updateSlide.bind(this));
+        global.workspace_manager.connect('notify::n-workspaces',
+                                         this._updateSlide.bind(this));
         this.actor.connect('notify::hover', this._updateSlide.bind(this));
         this._thumbnailsBox.actor.bind_property('visible', this.actor, 'visible', GObject.BindingFlags.SYNC_CREATE);
     },
 
     _getAlwaysZoomOut() {
-        // Always show the pager on hover or during a drag
-        let alwaysZoomOut = this.actor.hover || this._inDrag;
+        // Always show the pager on hover, during a drag, or if workspaces are
+        // actually used, e.g. there are windows on any non-active workspace
+        let workspaceManager = global.workspace_manager;
+        let alwaysZoomOut = this.actor.hover ||
+                            this._inDrag ||
+                            !Meta.prefs_get_dynamic_workspaces() ||
+                            workspaceManager.n_workspaces > 2 ||
+                            workspaceManager.get_active_workspace_index() != 0;
 
         if (!alwaysZoomOut) {
             let monitors = Main.layoutManager.monitors;