Add kAccessibilityFocusFallsbackToWidget property

ui/views/accessibility/ax_aura_obj_cache.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/accessibility/ax_aura_obj_cache.h"
 
 #include "base/memory/ptr_util.h"
 #include "base/memory/singleton.h"
 #include "ui/aura/client/focus_client.h"
 #include "ui/aura/window.h"
@@ skipping 142 matching lines @@
   if (!focused_widget)
     return nullptr;
 
   FocusManager* focus_manager = focused_widget->GetFocusManager();
   if (!focus_manager)
     return nullptr;
 
   View* focused_view = focus_manager->GetFocusedView();
   if (focused_view)
     return focused_view;
+
+  // If no view is focused, falls back to accessibility focusable root view.
+  View* root_view = focused_widget->GetRootView();
+  if (root_view != nullptr && root_view->IsAccessibilityFocusable())
+    return root_view;
   else
-    return focused_widget->GetRootView();
+    return nullptr;
 }
 
 void AXAuraObjCache::OnWindowFocused(aura::Window* gained_focus,
                                      aura::Window* lost_focus) {
   OnFocusedViewChanged();
 }
 
 void AXAuraObjCache::OnWindowDestroying(aura::Window* window) {
   focus_client_ = nullptr;
 }
@@ skipping 36 matching lines @@
     AuraView* aura_view,
     std::map<AuraView*, int32_t>& aura_view_to_id_map) {
   int32_t id = GetID(aura_view);
   if (id == -1)
     return;
   aura_view_to_id_map.erase(aura_view);
   Remove(id);
 }
 
 }  // namespace views