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

chrome/browser/resources/settings/appearance_page/home_url_input.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
  * `home-url-input` is a single-line text field intending to be used with
  * prefs.homepage
  */
 Polymer({
@@ skipping 116 matching lines @@
     return disabled || this.isPrefEnforced();
   },
 
   /** @private */
   validate_: function() {
     if (this.value == '') {
       this.invalid = false;
       return;
     }
 
-    this.browserProxy_.validateStartupPage(this.value).then(function(isValid) {
+    this.browserProxy_.validateStartupPage(this.value).then(isValid => {
       this.invalid = !isValid;
-    }.bind(this));
+    });
   },
 });