Splits ToplevelWindowEventHandler into two

ash/wm/common/wm_display_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_DISPLAY_OBSERVER_H_
 #define ASH_WM_COMMON_WM_DISPLAY_OBSERVER_H_
 
 #include "ash/wm/common/ash_wm_common_export.h"
 
 namespace ash {
 namespace wm {
 
 class WmWindow;
 
 // Used to track changes in display configuration.
 class ASH_WM_COMMON_EXPORT WmDisplayObserver {
  public:
+  virtual void OnDisplayConfigurationChanging() {}

[James Cook, 2016/05/21 18:28:21]

It's pedantic, but I would comment above this one that it's called before the
display config change, and comment below that it's after. I really like
documentation on interface classes.

[sky, 2016/05/23 15:48:52]

Done.

   virtual void OnDisplayConfigurationChanged() {}
 
  protected:
   virtual ~WmDisplayObserver() {}
 };
 
 }  // namespace wm
 }  // namespace ash
 
 #endif  // ASH_WM_COMMON_WM_DISPLAY_OBSERVER_H_