WebUI: Undo some usages of ES6 features that break uglify.

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview
  * 'settings-ui' implements the UI for the Settings page.
  *
  * Example:
  *
@@ skipping 193 matching lines @@
     // Trim leading whitespace only, to prevent searching for empty string. This
     // still allows the user to search for 'foo bar', while taking a long pause
     // after typing 'foo '.
     var query = e.detail.replace(/^\s+/, '');
     // Prevent duplicate history entries.
     if (query == this.lastSearchQuery_)
       return;
 
     settings.navigateTo(
         settings.Route.BASIC,
-        query.length > 0 ? new URLSearchParams(`search=${query}`) : undefined,
+        query.length > 0 ? new URLSearchParams('search=' + query) : undefined,
         /* removeSearch */ true);
   },
 
   /**
    * @param {Event} event
    * @private
    */
   onIronActivate_: function(event) {
     if (event.detail.item.id != 'advancedPage')
       this.$.drawer.closeDrawer();
   },
 
   /** @private */
   onMenuButtonTap_: function() {
     this.$.drawer.toggle();
   },
 
   /** @private */
   directionDelegateChanged_: function() {
     this.$.drawer.align = this.directionDelegate.isRtl() ?
         'right' : 'left';
   },
 });