cros: Dump login/lock/oobe JS error stack traces to logs.

chrome/browser/resources/chromeos/login/login_shared.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 Common OOBE controller methods. This method is shared between
  * OOBE, login, and the lock screen. Add only methods that need to be shared
  * between all *three* screens here, as each additional method increases the
  * time it takes to show the lock screen.
  *
@@ skipping 423 matching lines @@
          /text|password|search/.test(src.type);
 });
 
 
 (function() {
   'use strict';
 
   document.addEventListener('DOMContentLoaded', function() {
     Oobe.initialize();
   });
+
+  // Install a global error handler so stack traces are included in logs.
+  window.onerror = function(message, file, line, column, error) {
+    console.error(error.stack);
+  }
 })();