PERF: don't render the category list if we are not showing it.

app/assets/javascripts/discourse/components/category-drop.js.es6

@@ -57,6 +57,16 @@ export default Ember.Component.extend({
 
   actions: {
     expand: function() {
+      var self = this;
+
+      if(!this.get('renderCategories')){
+        this.set('renderCategories',true);
+        Em.run.next(function(){
+          self.send('expand');
+        });
+        return;
+      }
+
       if (this.get('expanded')) {
         this.close();
         return;
@@ -65,8 +75,7 @@ export default Ember.Component.extend({
       if (this.get('categories')) {
         this.set('expanded', true);
       }
-      var self = this,
-          $dropdown = this.$()[0];
+      var $dropdown = this.$()[0];
 
       this.$('a[data-drop-close]').on('click.category-drop', function() {
         self.close();

app/assets/javascripts/discourse/templates/components/category-drop.hbs

@@ -20,6 +20,8 @@
     {{#if subCategory}}
     <div class='cat'><a {{bind-attr href=noCategoriesUrl}} data-drop-close="true" class='badge-category home'>{{i18n categories.no_subcategory}}</a></div>
     {{/if}}
+    {{#if renderCategories}}
     {{#each categories}}<div class='cat'>{{category-link this allowUncategorized=true}}</div>{{/each}}
+    {{/if}}
   </section>
 {{/if}}