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

chrome/browser/resources/settings/controls/extension_controlled_indicator.js

 // Copyright 2016 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.
 
 Polymer({
   is: 'extension-controlled-indicator',
 
   behaviors: [I18nBehavior],
 
   properties: {
     extensionCanBeDisabled: Boolean,
     extensionId: String,
     extensionName: String,
   },
 
   /**
    * @param {string} extensionId
    * @param {string} extensionName
    * @return {string}
    * @private
    */
   getLabel_: function(extensionId, extensionName) {
     var manageUrl = 'chrome://extensions/?id=' + assert(this.extensionId);
     return this.i18n('controlledByExtension',
-        `<a href="${manageUrl}" target="_blank">` +
+        '<a href="' + manageUrl + '" target="_blank">' +
         assert(this.extensionName) + '</a>');
   },
 
   /** @private */
   onDisableTap_: function() {
     assert(this.extensionCanBeDisabled);
     settings.ExtensionControlBrowserProxyImpl.getInstance().disableExtension(
         assert(this.extensionId));
     this.fire('extension-disable');
   },
 });