cleanup: Disambiguate assignments in arrow functions

As arrow functions have an implicit return value, an assignment of
this.foo = bar could have been intended as a this.foo === bar
comparison. To catch those errors, we will disallow these kinds
of assignments unless they are marked explicitly by an extra pair
of parentheses.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/731

js/ui/windowManager.js

@@ -1114,7 +1114,7 @@ var WindowManager = class {
 
     _showPadOsd(display, device, settings, imagePath, editionMode, monitorIndex) {
         this._currentPadOsd = new PadOsd.PadOsd(device, settings, imagePath, editionMode, monitorIndex);
-        this._currentPadOsd.connect('closed', () => this._currentPadOsd = null);
+        this._currentPadOsd.connect('closed', () => (this._currentPadOsd = null));
 
         return this._currentPadOsd.actor;
     }