Adds OnChildWindowVisibilityChanged to ui::WindowObserver

ash/mus/workspace/workspace_layout_manager_unittest.cc

 // 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.
 
 #include "ash/common/wm/workspace/workspace_layout_manager.h"
 
 #include <string>
 #include <utility>
 
 #include "ash/common/shell_observer.h"
@@ skipping 506 matching lines @@
 // A WindowObserver which sets the focus when the window becomes visible.
 class FocusObserver : public ui::WindowObserver {
  public:
   explicit FocusObserver(ui::Window* window)
       : window_(window), show_state_(ui::SHOW_STATE_END) {
     window_->AddObserver(this);
   }
   ~FocusObserver() override { window_->RemoveObserver(this); }
 
   // aura::test::TestWindowDelegate overrides:
-  void OnWindowVisibilityChanged(ui::Window* window) override {
-    if (window_->visible())
+  void OnWindowVisibilityChanged(ui::Window* window, bool visible) override {
+    if (visible)
       window_->SetFocus();
     show_state_ = WmWindowMus::Get(window_)->GetShowState();
   }
 
   ui::WindowShowState GetShowStateAndReset() {
     ui::WindowShowState ret = show_state_;
     show_state_ = ui::SHOW_STATE_END;
     return ret;
   }
 
@@ skipping 550 matching lines @@
                       occluded_window_bounds.width(),
                       occluded_window_bounds.height()).ToString(),
             window->bounds().ToString());
   HideKeyboard();
   EXPECT_EQ(occluded_window_bounds.ToString(), window->bounds().ToString());
 }
 */
 
 }  // namespace mus
 }  // namespace ash