Clarify title of Add Supervision dialog for screen readers

Currently, screen readers narrate "Setup parental controls" for the
title of the Add Supervision dialog. This phrase is unclear and should
be changed to "Setup parental controls dialog" instead to describe the
top-level dialog more clearly when in focus.

Bug: 1011556
Change-Id: I82707b26c80354dfbe1395d8f3a33517be8231db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1842633Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Reviewed-by: Aga Wronska <agawronska@chromium.org>
Commit-Queue: Toby Huang <tobyhuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704860}

chrome/browser/resources/chromeos/add_supervision/add_supervision.html

@@ -62,7 +62,8 @@
             width: 100%;
           }
         </style>
-        <div id="offlineContentDiv">
+        <div id="offlineContentDiv" role="dialog"
+            aria-label="$i18n{pageTitle}">
           <div>
             <svg xmlns="http://www.w3.org/2000/svg" class="error-icon" width="32px" height="32px" viewBox="0 0 22 22">
               <path d="M11 15h2v2h-2v-2zm0-8h2v6h-2V7zm.99-5C6.47 2 2 6.48 2 12s4.47 10 9.99 10C17.52 22 22 17.52 22 12S17.52 2 11.99 2zM12 20c-4.42 0-8-3.58-8-8s3.58-8 8-8 8 3.58 8 8-3.58 8-8 8z">
@@ -81,7 +82,8 @@
             </cr-button>
           </div>
         </div>
-        <div id="webviewDiv">
+        <div id="webviewDiv" role="dialog"
+            aria-label="$i18n{pageTitle}">
           <webview id="webview"></webview>
         </div>
       </template>