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

chrome/browser/resources/settings/people_page/sync_page.js

Index: chrome/browser/resources/settings/people_page/sync_page.js
diff --git a/chrome/browser/resources/settings/people_page/sync_page.js b/chrome/browser/resources/settings/people_page/sync_page.js
index 18102cfbfe4f2211d7ab519fc4ed6fa7769ab6f0..88c71faa7587358ec75b7ca7936d0b90a1effba6 100644
--- a/chrome/browser/resources/settings/people_page/sync_page.js
+++ b/chrome/browser/resources/settings/people_page/sync_page.js
@@ -217,11 +217,11 @@ Polymer({
     // Focus the password input box if password is needed to start sync.
     if (this.syncPrefs.passphraseRequired) {
       // Wait for the dom-if templates to render and subpage to become visible.
-      listenOnce(document, 'show-container', function() {
+      listenOnce(document, 'show-container', () => {
         var input = /** @type {!PaperInputElement} */ (
             this.$$('#existingPassphraseInput'));
         input.inputElement.focus();
-      }.bind(this));
+      });
     }
   },