Fix AshWindowTreeHost shutdown for Ozone X11.

ui/ozone/platform/wayland/wayland_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 UI_OZONE_PLATFORM_WAYLAND_WAYLAND_WINDOW_H_
 #define UI_OZONE_PLATFORM_WAYLAND_WAYLAND_WINDOW_H_
 
 #include "ui/events/platform/platform_event_dispatcher.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/native_widget_types.h"
@@ skipping 25 matching lines @@
   // Set whether this window has pointer focus and should dispatch mouse events.
   void set_pointer_focus(bool focus) { has_pointer_focus_ = focus; }
 
   // Set whether this window has keyboard focus and should dispatch key events.
   void set_keyboard_focus(bool focus) { has_keyboard_focus_ = focus; }
 
   // PlatformWindow
   void Show() override;
   void Hide() override;
   void Close() override;
+  void PrepareForShutdown() override;
   void SetBounds(const gfx::Rect& bounds) override;
   gfx::Rect GetBounds() override;
   void SetTitle(const base::string16& title) override;
   void SetCapture() override;
   void ReleaseCapture() override;
   void ToggleFullscreen() override;
   void Maximize() override;
   void Minimize() override;
   void Restore() override;
   void SetCursor(PlatformCursor cursor) override;
@@ skipping 26 matching lines @@
   uint32_t pending_configure_serial_;
   bool has_pointer_focus_ = false;
   bool has_keyboard_focus_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(WaylandWindow);
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PLATFORM_WAYLAND_WAYLAND_WINDOW_H_