cleanup: Port non-GObject classes to JS6 classes

ES6 finally adds standard class syntax to the language, so we can
replace our custom Lang.Class framework with the new syntax. Any
classes that inherit from GObject will need special treatment,
so limit the port to regular javascript classes for now.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/361

js/ui/ctrlAltTab.js

@@ -2,7 +2,6 @@
 
 const Clutter = imports.gi.Clutter;
 const Gtk = imports.gi.Gtk;
-const Lang = imports.lang;
 const Meta = imports.gi.Meta;
 const Shell = imports.gi.Shell;
 const St = imports.gi.St;
@@ -21,15 +20,13 @@ var SortGroup = {
     BOTTOM: 2
 };
 
-var CtrlAltTabManager = new Lang.Class({
-    Name: 'CtrlAltTabManager',
-
-    _init() {
+var CtrlAltTabManager = class CtrlAltTabManager {
+    constructor() {
         this._items = [];
         this.addGroup(global.window_group, _("Windows"),
                       'focus-windows-symbolic', { sortGroup: SortGroup.TOP,
                                                   focusCallback: this._focusWindows.bind(this) });
-    },
+    }
 
     addGroup(root, name, icon, params) {
         let item = Params.parse(params, { sortGroup: SortGroup.MIDDLE,
@@ -44,7 +41,7 @@ var CtrlAltTabManager = new Lang.Class({
         root.connect('destroy', () => { this.removeGroup(root); });
         if (root instanceof St.Widget)
             global.focus_manager.add_group(root);
-    },
+    }
 
     removeGroup(root) {
         if (root instanceof St.Widget)
@@ -55,14 +52,14 @@ var CtrlAltTabManager = new Lang.Class({
                 return;
             }
         }
-    },
+    }
 
     focusGroup(item, timestamp) {
         if (item.focusCallback)
             item.focusCallback(timestamp);
         else
             item.root.navigate_focus(null, Gtk.DirectionType.TAB_FORWARD, false);
-    },
+    }
 
     // Sort the items into a consistent order; panel first, tray last,
     // and everything else in between, sorted by X coordinate, so that
@@ -77,7 +74,7 @@ var CtrlAltTabManager = new Lang.Class({
         [bx, y] = b.proxy.get_transformed_position();
 
         return ax - bx;
-    },
+    }
 
     popup(backward, binding, mask) {
         // Start with the set of focus groups that are currently mapped
@@ -130,22 +127,20 @@ var CtrlAltTabManager = new Lang.Class({
                                     this._popup = null;
                                 });
         }
-    },
+    }
 
     _focusWindows(timestamp) {
         global.display.focus_default_window(timestamp);
     }
-});
+};
 
-var CtrlAltTabPopup = new Lang.Class({
-    Name: 'CtrlAltTabPopup',
-    Extends: SwitcherPopup.SwitcherPopup,
-
-    _init(items) {
-        this.parent(items);
+var CtrlAltTabPopup =
+class CtrlAltTabPopup extends SwitcherPopup.SwitcherPopup {
+    constructor(items) {
+        super(items);
 
         this._switcherList = new CtrlAltTabSwitcher(this._items);
-    },
+    }
 
     _keyPressHandler(keysym, action) {
         if (action == Meta.KeyBindingAction.SWITCH_PANELS)
@@ -160,24 +155,22 @@ var CtrlAltTabPopup = new Lang.Class({
             return Clutter.EVENT_PROPAGATE;
 
         return Clutter.EVENT_STOP;
-    },
+    }
 
     _finish(time) {
-        this.parent(time);
+        super._finish(time);
         Main.ctrlAltTabManager.focusGroup(this._items[this._selectedIndex], time);
-    },
-});
+    }
+};
 
-var CtrlAltTabSwitcher = new Lang.Class({
-    Name: 'CtrlAltTabSwitcher',
-    Extends: SwitcherPopup.SwitcherList,
-
-    _init(items) {
-        this.parent(true);
+var CtrlAltTabSwitcher =
+class CtrlAltTabSwitcher extends SwitcherPopup.SwitcherList {
+    constructor(items) {
+        super(true);
 
         for (let i = 0; i < items.length; i++)
             this._addIcon(items[i]);
-    },
+    }
 
     _addIcon(item) {
         let box = new St.BoxLayout({ style_class: 'alt-tab-app',
@@ -195,4 +188,4 @@ var CtrlAltTabSwitcher = new Lang.Class({
 
         this.addItem(box, text);
     }
-});
+};