MD Settings: Convert all usages of .bind(this) to use ES6 arrow function.

chrome/browser/resources/settings/prefs/prefs.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-prefs' exposes a singleton model of Chrome settings and
  * preferences, which listens to changes to Chrome prefs whitelisted in
  * chrome.settingsPrivate. When changing prefs in this element's 'prefs'
  * property via the UI, the singleton model tries to set those preferences in
@@ skipping 227 matching lines @@
     if (!success)
       this.refresh(key);
   },
 
   /**
    * Get the current pref value from chrome.settingsPrivate to ensure the UI
    * stays up to date.
    * @param {string} key
    */
   refresh: function(key) {
-    this.settingsApi_.getPref(key, function(pref) {
+    this.settingsApi_.getPref(key, pref => {
       this.updatePrefs_([pref]);
-    }.bind(this));
+    });
   },
 
   /**
    * Updates the prefs model with the given prefs.
    * @param {!Array<!chrome.settingsPrivate.PrefObject>} newPrefs
    * @private
    */
   updatePrefs_: function(newPrefs) {
     // Use the existing prefs object or create it.
     var prefs = this.prefs || {};
@@ skipping 46 matching lines @@
     this.prefs = undefined;
     this.lastPrefValues_ = {};
     this.initialized_ = false;
     // Remove the listener added in initialize().
     this.settingsApi_.onPrefsChanged.removeListener(this.boundPrefsChanged_);
     this.settingsApi_ =
         /** @type {SettingsPrivate} */ (chrome.settingsPrivate);
   },
 });
 })();