Centralizes more shared code between ash and mash

ash/common/wm_window.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_COMMON_WM_WINDOW_H_
 #define ASH_COMMON_WM_WINDOW_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 136 matching lines @@
   // The implementation of this matches aura::Window::GetToplevelWindow().
   virtual WmWindow* GetToplevelWindow() = 0;
   // The implementation of this matches
   // aura::client::ActivationClient::GetToplevelWindow().
   virtual WmWindow* GetToplevelWindowForFocus() = 0;
 
   // See aura::client::ParentWindowWithContext() for details of what this does.
   virtual void SetParentUsingContext(WmWindow* context,
                                      const gfx::Rect& screen_bounds) = 0;
   virtual void AddChild(WmWindow* window) = 0;
+  virtual void RemoveChild(WmWindow* child) = 0;
 
   WmWindow* GetParent() {
     return const_cast<WmWindow*>(
         const_cast<const WmWindow*>(this)->GetParent());
   }
   virtual const WmWindow* GetParent() const = 0;
 
   WmWindow* GetTransientParent() {
     return const_cast<WmWindow*>(
         const_cast<const WmWindow*>(this)->GetTransientParent());
@@ skipping 159 matching lines @@
   virtual void AddLimitedPreTargetHandler(ui::EventHandler* handler) = 0;
   virtual void RemoveLimitedPreTargetHandler(ui::EventHandler* handler) = 0;
 
  protected:
   virtual ~WmWindow() {}
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_WM_WINDOW_H_