Call ShowRootWindow on NativeWindow's RootWindow to display the window.

ui/aura/window.cc

Index: ui/aura/window.cc
diff --git a/ui/aura/window.cc b/ui/aura/window.cc
index 9eec35c77f620fb283ee87a8f4ed227fc1b87f89..a3caa03af98753181e493b1d04f19aeff66c7b25 100644
--- a/ui/aura/window.cc
+++ b/ui/aura/window.cc
@@ -321,7 +321,7 @@ void Window::SetExternalTexture(ui::Texture* texture) {
 void Window::SetDefaultParentByRootWindow(RootWindow* root_window,
                                           const gfx::Rect& bounds_in_screen) {
   // TODO(erg): Enable this DCHECK once it is safe.
-  //  DCHECK(root_window);
+  DCHECK(root_window);
 
   // Stacking clients are mandatory on RootWindow objects.
   client::StackingClient* client = client::GetStackingClient(root_window);