[gnome-shell] switcherPopup: Implement functions to add and remove accessible states

[Florian Müllner <fmuellner src gnome org>]

commit bfb0bc7a291af8ba75ab3d8c99bc1616e08db536
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Thu Apr 26 11:19:40 2018 +0200

    switcherPopup: Implement functions to add and remove accessible states
    
    Set the accessible states of the switcherList items by calling a
    function instead of manipulating class-internal variables from outside
    the class, which is considered bad practice.
    
    The check whether the item at `_selectedIndex` exists can also be
    removed since we always select a new index after an item was removed
    (i.e. an app was closed) and destroy the alt-tab switcher right away if
    no more items exist (see `SwitcherPopup._itemRemovedHandler`).
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/167

 js/ui/altTab.js        | 5 ++---
 js/ui/switcherPopup.js | 8 ++++++++
 2 files changed, 10 insertions(+), 3 deletions(-)
---
diff --git a/js/ui/altTab.js b/js/ui/altTab.js
index 0130fa245d..12b7849399 100644
--- a/js/ui/altTab.js
+++ b/js/ui/altTab.js
@@ -365,8 +365,7 @@ class AppSwitcherPopup extends SwitcherPopup.SwitcherPopup {
             },
         });
         this._thumbnails = null;
-        if (this._switcherList._items[this._selectedIndex])
-            this._switcherList._items[this._selectedIndex].remove_accessible_state(Atk.StateType.EXPANDED);
+        this._switcherList.removeAccessibleState(this._selectedIndex, Atk.StateType.EXPANDED);
     }
 
     _createThumbnails() {
@@ -395,7 +394,7 @@ class AppSwitcherPopup extends SwitcherPopup.SwitcherPopup {
             },
         });
 
-        this._switcherList._items[this._selectedIndex].add_accessible_state(Atk.StateType.EXPANDED);
+        this._switcherList.addAccessibleState(this._selectedIndex, Atk.StateType.EXPANDED);
     }
 });
 
diff --git a/js/ui/switcherPopup.js b/js/ui/switcherPopup.js
index 5f2839cf2c..46a4b158ad 100644
--- a/js/ui/switcherPopup.js
+++ b/js/ui/switcherPopup.js
@@ -444,6 +444,14 @@ var SwitcherList = GObject.registerClass({
         this.emit('item-removed', index);
     }
 
+    addAccessibleState(index, state) {
+        this._items[index].add_accessible_state(state);
+    }
+
+    removeAccessibleState(index, state) {
+        this._items[index].remove_accessible_state(state);
+    }
+
     _onItemClicked(index) {
         this._itemActivated(index);
     }