Converts DockedWindowLayoutManager to common ash/wm types

ash/wm/common/wm_window_observer.h

 // Copyright 2016 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_WM_COMMON_WM_WINDOW_OBSERVER_H_
 #define ASH_WM_COMMON_WM_WINDOW_OBSERVER_H_
 
 #include "ash/ash_export.h"
 
 namespace gfx {
@@ skipping 24 matching lines @@
                                        intptr_t old) {}
 
   virtual void OnWindowStackingChanged(WmWindow* window) {}
 
   virtual void OnWindowDestroying(WmWindow* window) {}
 
   virtual void OnWindowBoundsChanged(WmWindow* window,
                                      const gfx::Rect& old_bounds,
                                      const gfx::Rect& new_bounds) {}
 
+  virtual void OnWindowVisibilityChanging(wm::WmWindow* window, bool visible) {}
+
  protected:
   virtual ~WmWindowObserver() {}
 };
 
 }  // namespace wm
 }  // namespace ash
 
 #endif  // ASH_WM_COMMON_WM_WINDOW_OBSERVER_H_