[MD settings] controlled by extension icon on default font size

ui/webui/resources/cr_elements/policy/cr_policy_pref_behavior.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 Behavior for policy controlled settings prefs.
  */
 
 /** @polymerBehavior */
 var CrPolicyPrefBehavior = {
   properties: {
     /**
      * Showing that an extension is controlling a pref is sometimes done with a
      * different UI (e.g. extension-controlled-indicator). In  those cases,
      * avoid showing an (extra) indicator here.
      * @public
      */
     ignoreExtensions: Boolean,
   },
 
   /**
    * Is the |pref| controlled by something that prevents user control of the
    * preference.
    * @return {boolean} True if |this.pref| is controlled by an enforced policy.
    */
   isPrefEnforced: function() {
+    if (!this.pref) {
+      return false;
+    }
     if (this.ignoreExtensions &&
         this.pref.controlledBy ==
             chrome.settingsPrivate.ControlledBy.EXTENSION) {
       return false;
     }
     return this.pref.enforcement == chrome.settingsPrivate.Enforcement.ENFORCED;
   },
 
   /**
    * @return {boolean} True if |this.pref| has a recommended or enforced policy.
    */
   hasPrefPolicyIndicator: function() {
     return this.isPrefEnforced() ||
         this.pref.enforcement == chrome.settingsPrivate.Enforcement.RECOMMENDED;
   },
 };