Accessibility changes to Supervised user error page.

This CL updates SupervisedUserErrorPage html page so that
users are notified when they have successfully request for permission.

This CL updates SupervisedUserErrorPage javascript so that
the focus moves away from the ghost button after request for permission.

Bug: 1045154, 1045148
Change-Id: I0e5c554b92af68794c9a12e3f97fd2c5d368e8f9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2024119
Commit-Queue: Yilkal Abe <yilkal@chromium.org>
Reviewed-by: Aga Wronska <agawronska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736254}

chrome/browser/supervised_user/supervised_user_error_page/resources/supervised_user_block_interstitial.html

@@ -21,8 +21,8 @@
     <div id="main-message">
       <h1 id="block-page-header">$i18n{blockPageHeader}</h1>
       <p id="block-page-message">$i18n{blockPageMessage}</p>
-      <h1 id="request-failed-message" hidden>$i18n{requestFailedMessage}</h1>
-      <h1 id="request-sent-message" hidden>$i18n{requestSentMessage}</h1>
+      <h1 id="request-failed-message" role="alert" hidden>$i18n{requestFailedMessage}</h1>
+      <h1 id="request-sent-message" role="alert" hidden>$i18n{requestSentMessage}</h1>
     </div>
     <div id="custodians-information" hidden>
       <div id="custodian-information" class="custodian-information">
@@ -58,7 +58,7 @@
     </button>
   </div>
   <div id="details" hidden>
-    <p id="details-header">$i18n{blockReasonHeader}</p>
+    <p id="details-header" role="alert" >$i18n{blockReasonHeader}</p>
     <p id="feedback">$i18nRaw{feedbackLink}</p>
   </div>
 </div>

chrome/browser/supervised_user/supervised_user_error_page/resources/supervised_user_block_interstitial.js

@@ -117,7 +117,10 @@ function initialize() {
  */
 function setRequestStatus(isSuccessful, isMainFrame) {
   console.log('setRequestStatus(' + isSuccessful +')');
-  requestCreated(isSuccessful, isMainFrame)
+  requestCreated(isSuccessful, isMainFrame);
+  if (isSuccessful) {
+    $('back-button').focus();
+  }
 }
 
 /**