Port message tray sources and notifications to class framework

Third step in the class framework port, now it's the turn of
MessageTray.Source and MessageTray.Notification, as well as
the various implementations around the shell.

https://bugzilla.gnome.org/show_bug.cgi?id=664436

js/ui/messageTray.js

@@ -408,11 +408,9 @@ Signals.addSignalMethods(FocusGrabber.prototype);
 // the content and the action area of the notification will be cleared.
 // The content area is also always cleared if 'customContent' is false
 // because it might contain the @banner that didn't fit in the banner mode.
-function Notification(source, title, banner, params) {
-    this._init(source, title, banner, params);
-}
+const Notification = new Lang.Class({
+    Name: 'Notification',
 
-Notification.prototype = {
     IMAGE_SIZE: 125,
 
     _init: function(source, title, banner, params) {
@@ -953,14 +951,12 @@ Notification.prototype = {
         this.actor.destroy();
         this.actor._delegate = null;
     }
-};
+});
 Signals.addSignalMethods(Notification.prototype);
 
-function Source(title) {
-    this._init(title);
-}
+const Source = new Lang.Class({
+    Name: 'MessageTraySource',
 
-Source.prototype = {
     ICON_SIZE: 24,
 
     _init: function(title) {
@@ -1142,7 +1138,7 @@ Source.prototype = {
     _lastNotificationRemoved: function() {
         this.destroy();
     }
-};
+});
 Signals.addSignalMethods(Source.prototype);
 
 function SummaryItem(source) {
@@ -2428,15 +2424,12 @@ MessageTray.prototype = {
     }
 };
 
-function SystemNotificationSource() {
-    this._init();
-}
-
-SystemNotificationSource.prototype = {
-    __proto__:  Source.prototype,
+const SystemNotificationSource = new Lang.Class({
+    Name: 'SystemNotificationSource',
+    Extends: Source,
 
     _init: function() {
-        Source.prototype._init.call(this, _("System Information"));
+        this.parent(_("System Information"));
 
         this._setSummaryIcon(this.createNotificationIcon());
     },
@@ -2450,4 +2443,4 @@ SystemNotificationSource.prototype = {
     open: function() {
         this.destroy();
     }
-};
+});