popupMenu: Introduce PopupDummyMenu

This is designed for things like the activities button that sort of
need a menu to make navigation work, but not really have it do anything.

https://bugzilla.gnome.org/show_bug.cgi?id=689109

js/ui/panel.js

@@ -599,11 +599,12 @@ const AppMenuButton = new Lang.Class({
 
             menu = new PopupMenu.RemoteMenu(this.actor, this._targetApp.menu, this._targetApp.action_group);
         } else {
-            if (this.menu && !(this.menu instanceof PopupMenu.RemoteMenu))
+            if (this.menu && this.menu.isDummyQuitMenu)
                 return;
 
             // fallback to older menu
             menu = new PopupMenu.PopupMenu(this.actor, 0.0, St.Side.TOP, 0);
+            menu.isDummyQuitMenu = true;
             menu.addAction(_("Quit"), Lang.bind(this, function() {
                 this._targetApp.request_quit();
             }));

js/ui/panelMenu.js

@@ -112,7 +112,7 @@ const Button = new Lang.Class({
         this.actor.connect('key-press-event', Lang.bind(this, this._onSourceKeyPress));
 
         if (dontCreateMenu)
-            this.menu = null;
+            this.menu = new PopupMenu.PopupDummyMenu(this.actor);
         else
             this.setMenu(new PopupMenu.PopupMenu(this.actor, menuAlignment, St.Side.TOP, 0));
 

js/ui/popupMenu.js

@@ -1274,6 +1274,27 @@ const PopupMenu = new Lang.Class({
     }
 });
 
+const PopupDummyMenu = new Lang.Class({
+    Name: 'PopupDummyMenu',
+
+    _init: function(sourceActor) {
+        this.sourceActor = sourceActor;
+        this.actor = sourceActor;
+        this.actor._delegate = this;
+    },
+
+    isChildMenu: function() {
+        return false;
+    },
+
+    open: function() { this.emit('open-state-changed', true); },
+    close: function() { this.emit('open-state-changed', false); },
+    destroy: function() {
+        this.emit('destroy');
+    },
+});
+Signals.addSignalMethods(PopupDummyMenu.prototype);
+
 const PopupSubMenu = new Lang.Class({
     Name: 'PopupSubMenu',
     Extends: PopupMenuBase,