Fix AshWindowTreeHost shutdown for Ozone X11.

ui/platform_window/win/win_window.cc

 // Copyright 2014 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/platform_window/win/win_window.h"
 
 #include <algorithm>
 #include <memory>
 
 #include "base/strings/string16.h"
@@ skipping 56 matching lines @@
 }
 
 void WinWindow::Hide() {
   ShowWindow(hwnd(), SW_HIDE);
 }
 
 void WinWindow::Close() {
   Destroy();
 }
 
+void WinWindow::PrepareForShutdown() {}
+
 void WinWindow::SetBounds(const gfx::Rect& bounds) {
   gfx::Rect window_bounds = GetWindowBoundsForClientBounds(
       GetWindowLong(hwnd(), GWL_STYLE),
       GetWindowLong(hwnd(), GWL_EXSTYLE),
       bounds);
   unsigned int flags = SWP_NOREPOSITION;
   if (!::IsWindowVisible(hwnd()))
     flags |= SWP_NOACTIVATE;
   SetWindowPos(hwnd(), NULL, window_bounds.x(), window_bounds.y(),
                window_bounds.width(), window_bounds.height(), flags);
@@ skipping 109 matching lines @@
 
 namespace test {
 
 // static
 void SetUsePopupAsRootWindowForTest(bool use) {
   use_popup_as_root_window_for_test = use;
 }
 
 }  // namespace test
 }  // namespace ui