Add null check when reporting changed nodes to an AX tree.

ui/views/accessibility/ax_window_obj_wrapper.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_window_obj_wrapper.h"
 
 #include <stddef.h>
 
 #include "base/strings/utf_string_conversions.h"
 #include "ui/accessibility/ax_node_data.h"
@@ skipping 78 matching lines @@
 
 void AXWindowObjWrapper::OnWindowHierarchyChanged(
     const HierarchyChangeParams& params) {
   if (params.phase == WindowObserver::HierarchyChangeParams::HIERARCHY_CHANGED)
     AXAuraObjCache::GetInstance()->Remove(params.target, params.old_parent);
 }
 
 void AXWindowObjWrapper::OnWindowBoundsChanged(aura::Window* window,
                                                const gfx::Rect& old_bounds,
                                                const gfx::Rect& new_bounds) {
-  if (window != window_)
+  if (window != window_ || !window->IsVisible())
     return;
 
   AXAuraObjCache::GetInstance()->FireEvent(this, ui::AX_EVENT_LOCATION_CHANGED);
 
   Widget* widget = Widget::GetWidgetForNativeView(window);
   if (widget) {
     views::View* root_view = widget->GetRootView();
     if (root_view)
       root_view->NotifyAccessibilityEvent(ui::AX_EVENT_LOCATION_CHANGED, true);
   }
 }
 
 void AXWindowObjWrapper::OnWindowPropertyChanged(aura::Window* window,
                                                  const void* key,
                                                  intptr_t old) {
-  if (window == window_ && key == ui::kChildAXTreeID) {
+  if (window == window_ && key == ui::kChildAXTreeID && window->IsVisible()) {
     AXAuraObjCache::GetInstance()->FireEvent(this,
                                              ui::AX_EVENT_CHILDREN_CHANGED);
   }
 }
 
 }  // namespace views