[Refactor] Move the logic to update bounds for show type from WorkspaceLayoutManager to DefaultState

ash/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_WM_WINDOW_STATE_OBSERVER_H_
 #define ASH_WM_WINDOW_STATE_OBSERVER_H_
 
 #include "ash/ash_export.h"
 #include "ash/wm/wm_types.h"
 
 namespace ash {
 namespace wm {
 class WindowState;
 
 class ASH_EXPORT WindowStateObserver {
  public:
-  // Called when the window's show type has changed. This is different from
-  // kWindowShowStatekey property change as this will be invoked when the window
+  // Following observer methods are different from kWindowShowStatekey
+  // property change as this will be invoked when the window
   // gets left/right maximized, and auto positioned. |old_type| is the value
   // before the change.
-  virtual void OnWindowShowTypeChanged(WindowState* window_state,
-                                       WindowShowType old_type) {}
+
+  // Called after the window's show 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.
+  virtual void OnPreWindowShowTypeChange(WindowState* window_state,
+                                         WindowShowType old_type) {}
+
+  // Called after the window's state has been changed for the new show type.
+  // This is used to update the shell state that depends on the update
+  // window bounds, such as shelf visibility.
+  virtual void OnPostWindowShowTypeChange(WindowState* window_state,
+                                          WindowShowType old_type) {}
 };
 
 }  // namespace wm
 }  // namespace ash
 
 #endif  // ASH_WM_WINDOW_STATE_OBSERVER_H_