Add kAccessibilityFocusFallsbackToWidget property

ui/views/accessibility/ax_aura_obj_cache.cc

Index: ui/views/accessibility/ax_aura_obj_cache.cc
diff --git a/ui/views/accessibility/ax_aura_obj_cache.cc b/ui/views/accessibility/ax_aura_obj_cache.cc
index 0ce0047c9987815064f5f795ccbb317198d53528..ad9df5c9fdd4d75a1b1e802c85352dd1de7f41f0 100644
--- a/ui/views/accessibility/ax_aura_obj_cache.cc
+++ b/ui/views/accessibility/ax_aura_obj_cache.cc
@@ -6,6 +6,8 @@
 
 #include "base/memory/ptr_util.h"
 #include "base/memory/singleton.h"
+#include "base/strings/string_util.h"
+#include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/focus_client.h"
 #include "ui/aura/window.h"
 #include "ui/views/accessibility/ax_aura_obj_wrapper.h"
@@ -160,8 +162,14 @@ View* AXAuraObjCache::GetFocusedView() {
   View* focused_view = focus_manager->GetFocusedView();
   if (focused_view)
     return focused_view;
-  else
+
+  if (focused_window->GetProperty(
+          aura::client::kAccessibilityFocusFallsbackToWidgetKey)) {
+    // If no view is focused, falls back to root view.
     return focused_widget->GetRootView();
+  }
+
+  return nullptr;
 }
 
 void AXAuraObjCache::OnWindowFocused(aura::Window* gained_focus,