UMA to track the reason for re-auth (draft).

chrome/browser/resources/chromeos/login/screen_password_changed.js

 // Copyright (c) 2012 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 Password changed screen implementation.
  */
 
 login.createScreen('PasswordChangedScreen', 'password-changed', function() {
   return {
@@ skipping 27 matching lines @@
             screen.classList.add('resync');
             $('password-changed-proceed-button').focus();
             $('password-changed').classList.remove('password-error');
             $('old-password').value = '';
             $('password-changed-ok-button').disabled = true;
           }
         });
 
       var gaiaPasswordChanged = $('gaia-password-changed');
       gaiaPasswordChanged.addEventListener('cancel', function(e) {
-          chrome.send('cancelPasswordChangedFlow');
+          chrome.send('cancelPasswordChangedFlow',
+              [$('gaia-password-changed').email]);
           gaiaPasswordChanged.reset();
         });
 
       gaiaPasswordChanged.addEventListener('passwordEnter', function(e) {
           chrome.send('migrateUserData', [e.detail.password]);
         });
 
       gaiaPasswordChanged.addEventListener('proceedAnyway', function() {
           chrome.send('resyncUserData');
         });
@@ skipping 76 matching lines @@
 
     get isNewGaiaFlow() {
       return document.querySelector('.new-gaia-flow') != undefined;
     },
 
     /**
      * Cancels password migration and drops the user back to the login screen.
      */
     cancel: function() {
       this.disabled = true;
-      chrome.send('cancelPasswordChangedFlow');
+      chrome.send('cancelPasswordChangedFlow', ['']);
     },
 
     /**
      * Starts migration process using old password that user provided.
      */
     migrate: function() {
       if (!$('old-password').value) {
         $('old-password').focus();
         return;
       }
@@ skipping 48 matching lines @@
       // It assumes session is about to start so hides login screen controls.
       Oobe.getInstance().headerHidden = false;
       Oobe.showScreen({id: SCREEN_PASSWORD_CHANGED});
       $('login-header-bar').signinUIState = SIGNIN_UI_STATE.PASSWORD_CHANGED;
       if (!this.isNewGaiaFlow)
         $('password-changed-ok-button').disabled = true;
     }
   };
 });