Adds OnChildWindowVisibilityChanged to ui::WindowObserver

ui/views/mus/native_widget_mus.h

 // Copyright 2015 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 UI_VIEWS_MUS_NATIVE_WIDGET_MUS_H_
 #define UI_VIEWS_MUS_NATIVE_WIDGET_MUS_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 242 matching lines @@
 
   // Returns true if this NativeWidgetMus exists on the window manager side
   // to provide the frame decorations.
   bool is_parallel_widget_in_window_manager() {
     return surface_type_ == ui::mojom::SurfaceType::UNDERLAY;
   }
 
   void set_last_cursor(ui::mojom::Cursor cursor) { last_cursor_ = cursor; }
   void SetShowState(ui::mojom::ShowState show_state);
 
-  void OnMusWindowVisibilityChanging(ui::Window* window);
-  void OnMusWindowVisibilityChanged(ui::Window* window);
+  void OnMusWindowVisibilityChanging(ui::Window* window, bool visible);
+  void OnMusWindowVisibilityChanged(ui::Window* window, bool visible);
 
   // Propagates the widget hit test mask, if any, to the ui::Window.
   // TODO(jamescook): Wire this through views::Widget so widgets can push
   // updates if needed.
   void UpdateHitTestMask();
 
   ui::Window* window_;
   ui::mojom::Cursor last_cursor_;
 
   internal::NativeWidgetDelegate* native_widget_delegate_;
@@ skipping 33 matching lines @@
   std::unique_ptr<TooltipManagerAura> tooltip_manager_;
 
   base::WeakPtrFactory<NativeWidgetMus> close_widget_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeWidgetMus);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_MUS_NATIVE_WIDGET_MUS_H_