Adds OnChildWindowVisibilityChanged to ui::WindowObserver

services/ui/public/cpp/window_observer.h

 // 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.
 
 #ifndef SERVICES_UI_PUBLIC_CPP_WINDOW_OBSERVER_H_
 #define SERVICES_UI_PUBLIC_CPP_WINDOW_OBSERVER_H_
 
 #include <stdint.h>
 
 #include <vector>
@@ skipping 46 matching lines @@
   virtual void OnWindowLostCapture(Window* window) {}
   virtual void OnWindowClientAreaChanged(
       Window* window,
       const gfx::Insets& old_client_area,
       const std::vector<gfx::Rect>& old_additional_client_areas) {}
 
   virtual void OnWindowFocusChanged(Window* gained_focus, Window* lost_focus) {}
 
   virtual void OnWindowPredefinedCursorChanged(Window* window,
                                                mojom::Cursor cursor) {}
-  virtual void OnWindowVisibilityChanging(Window* window) {}
-  virtual void OnWindowVisibilityChanged(Window* window) {}
+
+  // Changing the visibility of a window results in the following sequence of
+  // functions being called:
+  // . OnWindowVisibilityChanging(): called on observers added to the window
+  //    whose visibility is changing. This is called before the visibility has
+  //    changed internally.
+  // The following are called after the visibility changes:
+  // . OnChildWindowVisibilityChanged(): called on observers added to the
+  //   parent of the window whose visibility changed. This function is generally
+  //   intended for layout managers that need to do processing before
+  //   OnWindowVisibilityChanged() is called on observers of the window.
+  // . OnWindowVisibilityChanged(): called on observers added to the window
+  //   whose visibility changed, as well as observers added to all ancestors and
+  //   all descendants of the window.
+  virtual void OnWindowVisibilityChanging(Window* window, bool visible) {}
+  virtual void OnChildWindowVisibilityChanged(Window* window, bool visible) {}
+  virtual void OnWindowVisibilityChanged(Window* window, bool visible) {}
+
   virtual void OnWindowOpacityChanged(Window* window,
                                       float old_opacity,
                                       float new_opacity) {}
 
   // Invoked when this Window's shared properties have changed. This can either
   // be caused by SetSharedProperty() being called locally, or by us receiving
   // a mojo message that this property has changed. If this property has been
   // added, |old_data| is null. If this property was removed, |new_data| is
   // null.
   virtual void OnWindowSharedPropertyChanged(
@@ skipping 27 matching lines @@
   // allows the close it should destroy the window as appropriate.
   virtual void OnRequestClose(Window* window) {}
 
  protected:
   virtual ~WindowObserver() {}
 };
 
 }  // namespace ui
 
 #endif  // SERVICES_UI_PUBLIC_CPP_WINDOW_OBSERVER_H_