add testcase for js minify that produces $jscomp polyfills

with recent closure compiler default input language has changed from ES3 to ES6 produces $jscomp polyfills

tests/_test_files/js/jscomp.polyfill.js

@@ -0,0 +1,7 @@
+(function() {
+    /**
+     * @type {string}
+     */
+    var $array = jQuery.find('#div');
+    print($array.find('a'));
+})();

tests/_test_files/js/jscomp.polyfill.min.js

@@ -0,0 +1 @@
+(function(){var a=jQuery.find("#div");print(a.find("a"))})();