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

chrome/browser/resources/settings/appearance_page/appearance_page.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.
 
 /**
  * 'settings-appearance-page' is the settings page containing appearance
  * settings.
  *
  * Example:
  *
@@ skipping 212 matching lines @@
    * @private
    */
   themeChanged_: function(themeId, useSystemTheme) {
     if (themeId) {
       assert(!useSystemTheme);
 
       this.browserProxy_.getThemeInfo(themeId).then(function(info) {
         this.themeSublabel_ = info.name;
       }.bind(this));
 
-      this.themeUrl_ = `https://chrome.google.com/webstore/detail/${themeId}`;
+      this.themeUrl_ = 'https://chrome.google.com/webstore/detail/' + themeId;
       return;
     }
 
     var i18nId;
 // <if expr="is_linux and not chromeos">
     i18nId = useSystemTheme ? 'systemTheme' : 'classicTheme';
 // </if>
 // <if expr="not is_linux or chromeos">
     i18nId = 'chooseFromWebStore';
 // </if>
@@ skipping 19 matching lines @@
    * @see content::ZoomValuesEqual().
    * @param {number} zoom1
    * @param {number} zoom2
    * @return {boolean}
    * @private
    */
   zoomValuesEqual_: function(zoom1, zoom2) {
     return Math.abs(zoom1 - zoom2) <= 0.001;
   },
 });