attempt 2 at adjusting class definition so its more easily extensible

app/assets/javascripts/discourse/components/topic-footer-mobile-dropdown.js.es6

@@ -1,11 +1,15 @@
 import { iconHTML } from 'discourse-common/helpers/fa-icon';
 import Combobox from 'discourse-common/components/combo-box';
-import { on, observes } from 'ember-addons/ember-computed-decorators';
+import { observes } from 'ember-addons/ember-computed-decorators';
 
 export default Combobox.extend({
   none: "topic.controls",
 
-  @on('init')
+  init() {
+    this._super();
+    this._createContent();
+  },
+
   _createContent() {
     const content = [];
     const topic = this.get('topic');