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/misc/jsParse.js

@@ -172,7 +172,7 @@ function getPropertyNamesFromExpression(expr, commandHeader = '') {
 
         // Make sure propsUnique contains one key for every
         // property so we end up with a unique list of properties
-        allProps.map(p => propsUnique[p] = null);
+        allProps.map(p => (propsUnique[p] = null));
     }
     return Object.keys(propsUnique).sort();
 }