workspaceThumbnail: rebuild thumbnails if workareas size changed

https://bugzilla.gnome.org/show_bug.cgi?id=792687


(cherry picked from commit c29bd46e7a)

js/ui/workspaceThumbnail.js

@@ -673,11 +673,7 @@ var ThumbnailsBox = new Lang.Class({
         this._settings.connect('changed::dynamic-workspaces',
             this._updateSwitcherVisibility.bind(this));
 
-        Main.layoutManager.connect('monitors-changed', () => {
+        Main.layoutManager.connect('monitors-changed', this._rebuildThumbnails.bind(this));
-            this._destroyThumbnails();
-            if (Main.overview.visible)
-                this._createThumbnails();
-        });
     },
 
     _updateSwitcherVisibility() {
@@ -870,6 +866,9 @@ var ThumbnailsBox = new Lang.Class({
             Main.overview.connect('windows-restacked',
                                   this._syncStacking.bind(this));
 
+        this._workareasChangedId =
+            global.screen.connect('workareas-changed', this._rebuildThumbnails.bind(this));
+
         this._targetScale = 0;
         this._scale = 0;
         this._pendingScaleUpdate = false;
@@ -899,12 +898,24 @@ var ThumbnailsBox = new Lang.Class({
             this._syncStackingId = 0;
         }
 
+        if (this._workareasChangedId > 0) {
+            global.screen.disconnect(this._workareasChangedId);
+            this._workareasChangedId = 0;
+        }
+
         for (let w = 0; w < this._thumbnails.length; w++)
             this._thumbnails[w].destroy();
         this._thumbnails = [];
         this._porthole = null;
     },
 
+    _rebuildThumbnails() {
+        this._destroyThumbnails();
+
+        if (Main.overview.visible)
+            this._createThumbnails();
+    },
+
     _workspacesChanged() {
         let validThumbnails =
             this._thumbnails.filter(t => t.state <= ThumbnailState.NORMAL);