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

chrome/browser/resources/settings/site_settings/media_picker.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.
 
 /**
  * @fileoverview
  * 'media-picker' handles showing the dropdown allowing users to select the
  * default camera/microphone.
  */
 Polymer({
@@ skipping 32 matching lines @@
    */
   updateDevicesMenu_: function(type, devices, defaultDevice) {
     if (type != this.type)
       return;
 
     this.$.picker.hidden = devices.length == 0;
     if (devices.length > 0) {
       this.devices = devices;
 
       // Wait for <select> to be populated.
-      this.async(function() {
+      this.async(() => {
         this.$.mediaPicker.value = defaultDevice;
-      }.bind(this));
+      });
     }
   },
 
   /**
    * A handler for when an item is selected in the media picker.
    * @private
    */
   onChange_: function() {
     this.browserProxy.setDefaultCaptureDevice(
         this.type, this.$.mediaPicker.value);
   },
 });