Notify WindowStateObserver when minimizing in maximized mode.

ash/common/wm/window_state_observer.h

 // Copyright 2013 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_WINDOW_STATE_OBSERVER_H_
 #define ASH_COMMON_WM_WINDOW_STATE_OBSERVER_H_
 
 #include "ash/ash_export.h"
 #include "ash/common/wm/wm_types.h"
 
 namespace ash {
 namespace wm {
 class WindowState;
 
 class ASH_EXPORT WindowStateObserver {
  public:
+  virtual ~WindowStateObserver() {}
+
   // Following observer methods are different from kWindowShowStatekey
   // property change as they will be invoked when the window
   // gets left/right maximized, and auto positioned. |old_type| is the value
   // before the change.
 
   // Called after the window's state type is set to new type, but before
   // the window's bounds has been updated for the new type.
   // This is used to update the shell state such as work area so
   // that the window can use the correct environment to update its bounds.
   // TODO(oshima): Remove this once docked windows has its own state.
   virtual void OnPreWindowStateTypeChange(WindowState* window_state,
                                           WindowStateType old_type) {}
 
   // Called after the window's state has been updated.
   // This is used to update the shell state that depends on the updated
   // window bounds, such as shelf visibility.
   virtual void OnPostWindowStateTypeChange(WindowState* window_state,
                                            WindowStateType old_type) {}
 };
 
 }  // namespace wm
 }  // namespace ash
 
 #endif  // ASH_COMMON_WM_WINDOW_STATE_OBSERVER_H_