Send AX focus changed events for modal dialog open/close

Source/core/html/HTMLDialogElement.cpp

Index: Source/core/html/HTMLDialogElement.cpp
diff --git a/Source/core/html/HTMLDialogElement.cpp b/Source/core/html/HTMLDialogElement.cpp
index 82496b15abe91cb6fbcc2408c55bf128bd190be7..f4173a4e0b11d7b8b97a0c1e82a308078e2b8f4c 100644
--- a/Source/core/html/HTMLDialogElement.cpp
+++ b/Source/core/html/HTMLDialogElement.cpp
@@ -67,8 +67,13 @@ static void inertSubtreesChanged(Document& document)
     // it, though a more clever way is probably possible.
     Document* topDocument = document.topDocument();
     topDocument->clearAXObjectCache();
-    if (AXObjectCache* cache = topDocument->axObjectCache())
+    if (AXObjectCache* cache = topDocument->axObjectCache()) {
         cache->childrenChanged(cache->getOrCreate(topDocument));
+        // Screen readers appear to rely on focus to update their trees. Send
+        // one out in case one was queued up before the AX tree was cleared,
+        // rendering it meaningless.
+        cache->handleFocusedUIElementChanged(document);
+    }
 }
 
 HTMLDialogElement::HTMLDialogElement(Document& document)