cros: Add UMA metrics in migration UI to get more information from migration failures.

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

 // Copyright 2017 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.
 
 login.createScreen('EncryptionMigrationScreen', 'encryption-migration',
     function() {
   return {
     EXTERNAL_API: [
       'setUIState',
       'setMigrationProgress',
@@ skipping 10 matching lines @@
 
     /** @override */
     decorate: function() {
       var encryptionMigration = $('encryption-migration-element');
       encryptionMigration.addEventListener('upgrade', function() {
         chrome.send('startMigration');
       });
       encryptionMigration.addEventListener('skip', function() {
         chrome.send('skipMigration');
       });
-      encryptionMigration.addEventListener('restart', function() {
-        chrome.send('requestRestart');
+      encryptionMigration.addEventListener(
+          'restart-on-low-storage', function() {
+            chrome.send('requestRestartOnLowStorage');
+          });
+      encryptionMigration.addEventListener('restart-on-failure', function() {
+        chrome.send('requestRestartOnFailure');
       });
       encryptionMigration.addEventListener('openFeedbackDialog', function() {
         chrome.send('openFeedbackDialog');
       });
     },
 
     /**
      * Event handler that is invoked just before the screen in shown.
      */
     onBeforeShow: function() {
@@ skipping 59 matching lines @@
 
     /**
      * Updates the string representation of necessary space size.
      * @param {string} space
      */
     setNecessarySpaceInString: function(space) {
       $('encryption-migration-element').necessarySpaceInString = space;
     },
   };
 });