cros: Add spoken feedback for dynamically populated information in migration UI.

chrome/browser/resources/chromeos/login/encryption_migration.html

 <!-- 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. -->
 
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-progress/paper-progress.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
 <link rel="import" href="chrome://oobe/custom_elements.html">
@@ skipping 12 matching lines @@
           <h1 class="title">$i18n{migrationReadyTitle}</h1>
           <div class="subtitle">$i18n{migrationReadyDescription}</div>
         </div>
         <template is="dom-if" if="[[isEnoughBattery]]">
           <div class="footer layout vertical center">
             <img srcset="images/security_update_1x.png 1x,
                          images/security_update_2x.png 2x">
           </div>
         </template>
         <template is="dom-if" if="[[!isEnoughBattery]]">
-          <div class="footer layout vertical">
+          <div class="footer layout vertical" aria-live="polite">
             <div class="warning">
               [[computeBatteryWarningLabel_(batteryPercent)]]
             </div>
             <template is="dom-if" if="[[isCharging]]">
               <div>$i18n{migrationChargingLabel}</div>
             </template>
             <template is="dom-if" if="[[!isCharging]]">
               <div>$i18n{migrationAskChargeMessage}</div>
             </template>
             <div>[[computeNecessaryBatteryLevelLabel_()]]</div>
@@ skipping 19 matching lines @@
         <iron-icon class="oobe-icon chrome-logo"></iron-icon>
         <div class="header">
           <h1 class="title">$i18n{migrationMigratingTitle}</h1>
           <div class="subtitle">$i18n{migrationMigratingDescription}</div>
         </div>
         <div class="footer flex layout vertical">
           <paper-progress value="[[progress]]" max="1" step="0.001"
               indeterminate="[[isProgressIndeterminate_(progress)]]">
           </paper-progress>
           <template is="dom-if" if="[[!isProgressIndeterminate_(progress)]]">
-            <div>[[computeProgressLabel_(progress)]]</div>
+            <div aria-live="polite">[[computeProgressLabel_(progress)]]</div>
           </template>
         </div>
       </oobe-dialog>
     </template>
     <template is="dom-if" if="[[isMigrationFailed_(uiState)]]">
       <oobe-dialog tabindex="0" has-buttons>
         <iron-icon icon="cr:warning" class="oobe-icon warning"></iron-icon>
         <div class="header">
           <h1 class="title">$i18n{migrationFailedTitle}</h1>
           <div class="subtitle">$i18n{migrationFailedSubtitle}</div>
@@ skipping 12 matching lines @@
         </div>
       </oobe-dialog>
     </template>
     <template is="dom-if" if="[[isNotEnoughSpace_(uiState)]]">
       <oobe-dialog tabindex="0" has-buttons>
         <iron-icon class="oobe-icon chrome-logo"></iron-icon>
         <div class="header">
           <h1 class="title">$i18n{migrationReadyTitle}</h1>
           <div class="subtitle">$i18n{migrationReadyDescription}</div>
         </div>
-        <div class="footer layout vertical">
+        <div class="footer layout vertical" aria-live="polite">
           <div class="warning">$i18n{migrationNospaceWarningLabel}</div>
           <div>$i18n{migrationAskFreeSpaceMessage}</div>
           <div>[[computeAvailableSpaceLabel_(availableSpaceInString)]]</div>
           <div>[[computeNecessarySpaceLabel_(necessarySpaceInString)]]</div>
         </div>
         <div class="bottom-buttons flex layout horizontal">
           <div class="flex"></div>
           <template is="dom-if" if="[[!isResuming]]">
             <oobe-text-button inverse on-tap="onSkip_">
               <div>$i18n{migrationButtonContinue}</div>
             </oobe-text-button>
           </template>
           <template is="dom-if" if="[[isResuming]]">
             <oobe-text-button inverse on-tap="onRestart_">
               <div>$i18n{migrationButtonRestart}</div>
             </oobe-text-button>
           </template>
         </div>
       </oobe-dialog>
     </template>
   </template>
 </dom-module>