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

ui/views/accessibility/ax_window_obj_wrapper.cc

Index: ui/views/accessibility/ax_window_obj_wrapper.cc
diff --git a/ui/views/accessibility/ax_window_obj_wrapper.cc b/ui/views/accessibility/ax_window_obj_wrapper.cc
index c05bab373e4886a68a5d80ecbf8a7d64b307e765..e4001154ca39d49767275fe6bbc1f93eef771cce 100644
--- a/ui/views/accessibility/ax_window_obj_wrapper.cc
+++ b/ui/views/accessibility/ax_window_obj_wrapper.cc
@@ -96,7 +96,7 @@ void AXWindowObjWrapper::OnWindowHierarchyChanged(
 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);
@@ -112,7 +112,7 @@ void AXWindowObjWrapper::OnWindowBoundsChanged(aura::Window* window,
 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);
   }