Fix use after free when handling async touch events

ui/views/widget/desktop_aura/desktop_root_window_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_root_window_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 747 matching lines @@
   return false;
 }
 
 bool DesktopRootWindowHostWin::HandleUntranslatedKeyEvent(
     const ui::KeyEvent& event) {
   scoped_ptr<ui::KeyEvent> duplicate_event(event.Copy());
   return static_cast<aura::RootWindowHostDelegate*>(root_window_)->
       OnHostKeyEvent(duplicate_event.get());
 }
 
-bool DesktopRootWindowHostWin::HandleTouchEvent(
+void DesktopRootWindowHostWin::HandleTouchEvent(
     const ui::TouchEvent& event) {
-  return root_window_host_delegate_->OnHostTouchEvent(
+  // HWNDMessageHandler asynchronously processes touch events. Because of this
+  // it's possible for the aura::RootWindow to have been destroyed by the time
+  // we attempt to process them.
+  if (!GetWidget()->GetNativeView())
+    return;
+  root_window_host_delegate_->OnHostTouchEvent(
       const_cast<ui::TouchEvent*>(&event));
 }
 
 bool DesktopRootWindowHostWin::HandleIMEMessage(UINT message,
                                                 WPARAM w_param,
                                                 LPARAM l_param,
                                                 LRESULT* result) {
   MSG msg = {};
   msg.hwnd = GetHWND();
   msg.message = message;
@@ skipping 70 matching lines @@
 DesktopRootWindowHost* DesktopRootWindowHost::Create(
     internal::NativeWidgetDelegate* native_widget_delegate,
     DesktopNativeWidgetAura* desktop_native_widget_aura,
     const gfx::Rect& initial_bounds) {
   return new DesktopRootWindowHostWin(native_widget_delegate,
                                       desktop_native_widget_aura,
                                       initial_bounds);
 }
 
 }  // namespace views