Add status role to cleanup page title

This fixes two accessibility issues:
 - title not updated when state changes;
 - focus changed to the end of the page when UI is updated.

Bug: 806324
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I8a274a96b1bb5fabca8278e8241d91fb0a4be93c
Reviewed-on: https://chromium-review.googlesource.com/889578Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Fabio Tirelo <ftirelo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532231}

chrome/browser/resources/settings/chrome_cleanup_page/chrome_cleanup_page.html

@@ -84,7 +84,7 @@
         </iron-icon>
       </div>
       <div class="start">
-        <div>[[title_]]</div>
+        <div role="status">[[title_]]</div>
         <div hidden="[[!showExplanation_]]">
           <span class="secondary">[[explanation_]]</span>
           <a id="learn-more" href="$i18n{chromeCleanupLearnMoreUrl}"