TF-2533 part 3 replace beforeunload with pagehide

core/lib/presentation/views/html_viewer/html_content_viewer_on_web_widget.dart

@@ -147,7 +147,7 @@ class _HtmlContentViewerOnWebState extends State<HtmlContentViewerOnWeb> {
         window.parent.addEventListener('message', handleMessage, false);
         window.addEventListener('click', handleOnClickLink, true);
         window.addEventListener('load', handleOnLoad);
-        window.addEventListener('beforeunload', (event) => {
+        window.addEventListener('pagehide', (event) => {
           window.parent.removeEventListener('message', handleMessage, false);
         });