Attempt at fixing crash where compositor is null

ui/views/widget/desktop_aura/desktop_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/views/widget/desktop_aura/desktop_window_tree_host_win.h"
 
 #include "base/win/metro.h"
 #include "third_party/skia/include/core/SkPath.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/aura/client/aura_constants.h"
@@ skipping 846 matching lines @@
   desktop_native_widget_aura_->input_method_event_filter()->
       input_method()->OnInputLocaleChanged();
 }
 
 bool DesktopWindowTreeHostWin::HandlePaintAccelerated(
     const gfx::Rect& invalid_rect) {
   return native_widget_delegate_->OnNativeWidgetPaintAccelerated(invalid_rect);
 }
 
 void DesktopWindowTreeHostWin::HandlePaint(gfx::Canvas* canvas) {
-  compositor()->ScheduleRedrawRect(gfx::Rect());
+  // It appears possible to get WM_PAINT after WM_DESTROY.
+  if (compositor())
+    compositor()->ScheduleRedrawRect(gfx::Rect());
 }
 
 bool DesktopWindowTreeHostWin::HandleTooltipNotify(int w_param,
                                                    NMHDR* l_param,
                                                    LRESULT* l_result) {
   return tooltip_ && tooltip_->HandleNotify(w_param, l_param, l_result);
 }
 
 void DesktopWindowTreeHostWin::HandleTooltipMouseMove(UINT message,
                                                       WPARAM w_param,
@@ skipping 73 matching lines @@
 
 // static
 DesktopWindowTreeHost* DesktopWindowTreeHost::Create(
     internal::NativeWidgetDelegate* native_widget_delegate,
     DesktopNativeWidgetAura* desktop_native_widget_aura) {
   return new DesktopWindowTreeHostWin(native_widget_delegate,
                                       desktop_native_widget_aura);
 }
 
 }  // namespace views