Fix use after free when handling async touch events

ui/views/widget/desktop_aura/desktop_root_window_host_win.cc

Index: ui/views/widget/desktop_aura/desktop_root_window_host_win.cc
diff --git a/ui/views/widget/desktop_aura/desktop_root_window_host_win.cc b/ui/views/widget/desktop_aura/desktop_root_window_host_win.cc
index d81aeb84a9b4c8d70f7811cdd61d019d2a58f52e..63f6be3f504a3bb56f16ee703610531b23a44bd3 100644
--- a/ui/views/widget/desktop_aura/desktop_root_window_host_win.cc
+++ b/ui/views/widget/desktop_aura/desktop_root_window_host_win.cc
@@ -765,9 +765,14 @@ bool DesktopRootWindowHostWin::HandleUntranslatedKeyEvent(
       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));
 }