Use WmLayoutManager::OnChildWindowVisibilityChanged to update the system modal state.

ash/common/wm/system_modal_container_layout_manager.h

 // Copyright (c) 2012 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.
 
 #ifndef ASH_COMMON_WM_SYSTEM_MODAL_CONTAINER_LAYOUT_MANAGER_H_
 #define ASH_COMMON_WM_SYSTEM_MODAL_CONTAINER_LAYOUT_MANAGER_H_
 
 #include <memory>
 #include <set>
 #include <vector>
@@ skipping 18 matching lines @@
     : public wm::WmSnapToPixelLayoutManager,
       public WmWindowObserver,
       public keyboard::KeyboardControllerObserver {
  public:
   explicit SystemModalContainerLayoutManager(WmWindow* container);
   ~SystemModalContainerLayoutManager() override;
 
   bool has_window_dimmer() const { return window_dimmer_ != nullptr; }
 
   // Overridden from WmSnapToPixelLayoutManager:
+  void OnChildWindowVisibilityChanged(WmWindow* child, bool visible) override;
   void OnWindowResized() override;
   void OnWindowAddedToLayout(WmWindow* child) override;
   void OnWillRemoveWindowFromLayout(WmWindow* child) override;
   void SetChildBounds(WmWindow* child,
                       const gfx::Rect& requested_bounds) override;
 
   // Overridden from WmWindowObserver:
   void OnWindowPropertyChanged(WmWindow* window,
                                WmWindowProperty property) override;
-  void OnWindowVisibilityChanged(WmWindow* window, bool visible) override;
 
   // Overridden from keyboard::KeyboardControllerObserver:
   void OnKeyboardBoundsChanging(const gfx::Rect& new_bounds) override;
   void OnKeyboardClosed() override;
 
   // True if the window is either contained by the top most modal window,
   // or contained by its transient children.
   bool IsPartOfActiveModalWindow(WmWindow* window);
 
   // Activates next modal window if any. Returns false if there
@@ skipping 47 matching lines @@
   // Windows contained in this set are centered. Windows are automatically
   // added to this based on IsBoundsCentered().
   std::set<const WmWindow*> windows_to_center_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemModalContainerLayoutManager);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_WM_SYSTEM_MODAL_CONTAINER_LAYOUT_MANAGER_H_