Fix AshWindowTreeHost shutdown for Ozone X11.

ui/ozone/platform/wayland/wayland_window.cc

 // 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.
 
 #include "ui/ozone/platform/wayland/wayland_window.h"
 
 #include <xdg-shell-unstable-v5-client-protocol.h>
 
 #include "base/bind.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 63 matching lines @@
 void WaylandWindow::Show() {}
 
 void WaylandWindow::Hide() {
   NOTIMPLEMENTED();
 }
 
 void WaylandWindow::Close() {
   NOTIMPLEMENTED();
 }
 
+void WaylandWindow::PrepareForShutdown() {}
+
 void WaylandWindow::SetBounds(const gfx::Rect& bounds) {
   if (bounds == bounds_)
     return;
   bounds_ = bounds;
   delegate_->OnBoundsChanged(bounds);
 }
 
 gfx::Rect WaylandWindow::GetBounds() {
   return bounds_;
 }
@@ skipping 83 matching lines @@
   window->pending_bounds_ = gfx::Rect(0, 0, width, height);
   window->pending_configure_serial_ = serial;
 }
 
 // static
 void WaylandWindow::Close(void* data, xdg_surface* obj) {
   NOTIMPLEMENTED();
 }
 
 }  // namespace ui