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/windowAttentionHandler.js

@@ -1,27 +1,24 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 
-const Lang = imports.lang;
 const Shell = imports.gi.Shell;
 
 const Main = imports.ui.main;
 const MessageTray = imports.ui.messageTray;
 
-var WindowAttentionHandler = new Lang.Class({
-    Name: 'WindowAttentionHandler',
-
-    _init() {
+var WindowAttentionHandler = class {
+    constructor() {
         this._tracker = Shell.WindowTracker.get_default();
         this._windowDemandsAttentionId = global.display.connect('window-demands-attention',
                                                                 this._onWindowDemandsAttention.bind(this));
         this._windowMarkedUrgentId = global.display.connect('window-marked-urgent',
                                                                 this._onWindowDemandsAttention.bind(this));
-    },
+    }
 
     _getTitleAndBanner(app, window) {
         let title = app.get_name();
         let banner = _("“%s” is ready").format(window.get_title());
         return [title, banner]
-    },
+    }
 
     _onWindowDemandsAttention(display, window) {
         // We don't want to show the notification when the window is already focused,
@@ -54,18 +51,15 @@ var WindowAttentionHandler = new Lang.Class({
             notification.update(title, banner);
         }));
     }
-});
+};
 
-var Source = new Lang.Class({
-    Name: 'WindowAttentionSource',
-    Extends: MessageTray.Source,
+var Source = class WindowAttentionSource extends MessageTray.Source {
+    constructor(app, window) {
+        super(app.get_name());
 
-    _init(app, window) {
         this._window = window;
         this._app = app;
 
-        this.parent(app.get_name());
-
         this.signalIDs = [];
         this.signalIDs.push(this._window.connect('notify::demands-attention',
                                                  this._sync.bind(this)));
@@ -77,20 +71,20 @@ var Source = new Lang.Class({
                                                  () => { this.destroy(); }));
 
         this.connect('destroy', this._onDestroy.bind(this));
-    },
+    }
 
     _sync() {
         if (this._window.demands_attention || this._window.urgent)
             return;
         this.destroy();
-    },
+    }
 
     _onDestroy() {
         for(let i = 0; i < this.signalIDs.length; i++) {
            this._window.disconnect(this.signalIDs[i]);
         }
         this.signalIDs = [];
-    },
+    }
 
     _createPolicy() {
         if (this._app && this._app.get_app_info()) {
@@ -99,14 +93,14 @@ var Source = new Lang.Class({
         } else {
             return new MessageTray.NotificationGenericPolicy();
         }
-    },
+    }
 
     createIcon(size) {
         return this._app.create_icon_texture(size);
-    },
+    }
 
     open() {
         Main.activateWindow(this._window);
         this.destroy();
     }
-});
+};