workspaceThumbnail: Pass MetaWindow to _updateDialogPosition

This function was mistakenly called with a MetaWindow as first
argument inside the ::position-changed callback, instead of a
MetaWindowActor as it should.

However, that function quickly grabs the MetaWindow from the
actor, and all calling places have the MetaWindow readily available,
so switch to handing it as first function parameter.

Fixes warnings on ::position-changed, because of the aforementioned
typo.

js/ui/workspace.js

@@ -110,6 +110,7 @@ var WindowClone = new Lang.Class({
         this.metaWindow = realWindow.meta_window;
         this.metaWindow._delegate = this;
         this._workspace = workspace;
+        this._attachedDialogs = [];
 
         this._windowClone = new Clutter.Clone({ source: realWindow });
         // We expect this.actor to be used for all interaction rather than
@@ -208,6 +209,12 @@ var WindowClone = new Lang.Class({
     },
 
     addDialog(win) {
+        let realWin = win.get_compositor_private();
+        if (this._attachedDialogs.includes(realWin))
+            return;
+
+        this._attachedDialogs.push(realWin);
+
         let parent = win.get_transient_for();
         while (parent.is_attached_dialog())
             parent = parent.get_transient_for();
@@ -225,7 +232,7 @@ var WindowClone = new Lang.Class({
     },
 
     hasAttachedDialogs() {
-        return this.actor.get_n_children() > 1;
+        return this._attachedDialogs.length > 1;
     },
 
     _doAddAttachedDialog(metaWin, realWin) {
@@ -235,6 +242,9 @@ var WindowClone = new Lang.Class({
         clone._posChangedId = metaWin.connect('position-changed',
             this._onMetaWindowSizeChanged.bind(this));
         clone._destroyId = realWin.connect('destroy', () => {
+            let idx = this._attachedDialogs.indexOf(realWin);
+            this._attachedDialogs.splice(idx, 1);
+
             clone.destroy();
 
             this._onMetaWindowSizeChanged();

js/ui/workspaceThumbnail.js

@@ -151,7 +151,7 @@ var WindowClone = new Lang.Class({
 
     _doAddAttachedDialog(metaDialog, realDialog) {
         let clone = new Clutter.Clone({ source: realDialog });
-        this._updateDialogPosition(realDialog, clone);
+        this._updateDialogPosition(metaDialog, clone);
 
         clone._updateId = realDialog.connect('notify::position', dialog => {
             this._updateDialogPosition(dialog, clone);
@@ -162,8 +162,7 @@ var WindowClone = new Lang.Class({
         this.actor.add_child(clone);
     },
 
-    _updateDialogPosition(realDialog, cloneDialog) {
+    _updateDialogPosition(metaDialog, cloneDialog) {
-        let metaDialog = realDialog.meta_window;
         let dialogRect = metaDialog.get_frame_rect();
         let rect = this.metaWindow.get_frame_rect();