[MD settings] keep side nav open on advanced click

This CL keeps the side nav (sidebar) open when the advanced submenu is
toggled. (Fixes regression).

BUG=None (follow up to cl 2651103003)
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2659593004
Cr-Commit-Position: refs/heads/master@{#446521}

chrome/browser/resources/settings/settings_ui/settings_ui.js

@@ -220,7 +220,7 @@ Polymer({
    * @private
    */
   onIronActivate_: function(event) {
-    if (event.detail.item.id != 'advancedPage')
+    if (event.detail.item.id != 'advancedSubmenu')
       this.$.drawer.closeDrawer();
   },