Remove PrepareForShutdown

ui/aura/window_tree_host_win.cc

 // Copyright (c) 2012 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/aura/window_tree_host_win.h"
 
 #include <windows.h>
 
 #include <algorithm>
 
@@ skipping 207 matching lines @@
 void WindowTreeHostWin::PostNativeEvent(const base::NativeEvent& native_event) {
   ::PostMessage(
       hwnd(), native_event.message, native_event.wParam, native_event.lParam);
 }
 
 void WindowTreeHostWin::OnDeviceScaleFactorChanged(
     float device_scale_factor) {
   NOTIMPLEMENTED();
 }
 
-void WindowTreeHostWin::PrepareForShutdown() {
-  NOTIMPLEMENTED();
-}
-
 ui::EventProcessor* WindowTreeHostWin::GetEventProcessor() {
   return dispatcher();
 }
 
 void WindowTreeHostWin::OnClose() {
   // TODO: this obviously shouldn't be here.
   base::MessageLoopForUI::current()->Quit();
 }
 
 LRESULT WindowTreeHostWin::OnKeyEvent(UINT message,
@@ skipping 62 matching lines @@
 namespace test {
 
 // static
 void SetUsePopupAsRootWindowForTest(bool use) {
   use_popup_as_root_window_for_test = use;
 }
 
 }  // namespace test
 
 }  // namespace aura