Remove PrepareForShutdown

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.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/views/widget/desktop_aura/desktop_window_tree_host_x11.h"
 
 #include <X11/extensions/shape.h>
 #include <X11/extensions/XInput2.h>
 #include <X11/Xatom.h>
 #include <X11/Xregion.h>
@@ skipping 885 matching lines @@
     default:
       break;
   }
   XSendEvent(xdisplay_, xwindow_, False, 0, &xevent);
 }
 
 void DesktopWindowTreeHostX11::OnDeviceScaleFactorChanged(
     float device_scale_factor) {
 }
 
-void DesktopWindowTreeHostX11::PrepareForShutdown() {
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopWindowTreeHostX11, ui::EventSource implementation:
 
 ui::EventProcessor* DesktopWindowTreeHostX11::GetEventProcessor() {
   return dispatcher();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopWindowTreeHostX11, private:
 
@@ skipping 673 matching lines @@
   if (linux_ui) {
     ui::NativeTheme* native_theme = linux_ui->GetNativeTheme();
     if (native_theme)
       return native_theme;
   }
 
   return ui::NativeTheme::instance();
 }
 
 }  // namespace views