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

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

Index: chrome/browser/resources/chromeos/login/encryption_migration.html
diff --git a/chrome/browser/resources/chromeos/login/encryption_migration.html b/chrome/browser/resources/chromeos/login/encryption_migration.html
index da40f3b52910d7fc79d1efd4cfb8d69a7ec4c193..2dd79466cfd4f6bd2e570653d5a041a0219304c5 100644
--- a/chrome/browser/resources/chromeos/login/encryption_migration.html
+++ b/chrome/browser/resources/chromeos/login/encryption_migration.html
@@ -30,7 +30,7 @@
           </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>
@@ -70,7 +70,7 @@
               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>
@@ -103,7 +103,7 @@
           <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>