Wait for the battery level before starting encryption migration.

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',
       'setIsResuming',
+      'setBatteryPercent',
     ],
 
     /**
      * Ignore any accelerators the user presses on this screen.
      */
     ignoreAccelerators: true,
 
     /** @override */
     decorate: function() {
       var encryptionMigration = $('encryption-migration-element');
@@ skipping 38 matching lines @@
     },
 
     /**
      * Updates the migration screen based on whether the migration process is
      * resuming the previous one.
      * @param {boolean} isResuming
      */
     setIsResuming: function(isResuming) {
       $('encryption-migration-element').isResuming = isResuming;
     },
+
+    /**
+     * Updates battery level of the device.
+     * @param {number} batteryPercent Battery level in percent.
+     * @param {boolean} isEnoughBattery True if the battery is enough.
+     */
+    setBatteryPercent: function(batteryPercent, isEnoughBattery) {
+      $('encryption-migration-element').batteryPercent =
+          Math.floor(batteryPercent);
+      $('encryption-migration-element').isEnoughBattery = isEnoughBattery;
+    },
   };
 });