Reland: mus: Enable system modal windows

mash/example/window_type_launcher/window_type_launcher.cc

Index: mash/example/window_type_launcher/window_type_launcher.cc
diff --git a/mash/example/window_type_launcher/window_type_launcher.cc b/mash/example/window_type_launcher/window_type_launcher.cc
index 76efffcb16c79ae1fc0bc5cb3f9654aa4aece323..0f5d5f488754beb3ffda50c1d31252caf6e7291a 100644
--- a/mash/example/window_type_launcher/window_type_launcher.cc
+++ b/mash/example/window_type_launcher/window_type_launcher.cc
@@ -48,14 +48,14 @@ class ModalWindow : public views::WidgetDelegateView,
                                             base::ASCIIToUTF16("Moar!"))) {
     ++g_color_index %= arraysize(g_colors);
     open_button_->SetStyle(views::Button::STYLE_BUTTON);
+    open_button_->SetVisible(modal_type != ui::MODAL_TYPE_SYSTEM);
     AddChildView(open_button_);
   }
   ~ModalWindow() override {}
 
   static void OpenModalWindow(aura::Window* parent, ui::ModalType modal_type) {
-    views::Widget* widget =
-        views::Widget::CreateWindowWithParent(new ModalWindow(modal_type),
-                                              parent);
+    views::Widget* widget = views::Widget::CreateWindowWithParent(
+        new ModalWindow(modal_type), parent);
     widget->GetNativeView()->SetName("ModalWindow");
     widget->Show();
   }
@@ -308,8 +308,7 @@ class WindowTypeLauncherView : public views::WidgetDelegateView,
       NOTIMPLEMENTED();
     }
     else if (sender == system_modal_button_) {
-      ModalWindow::OpenModalWindow(GetWidget()->GetNativeView(),
-                                   ui::MODAL_TYPE_SYSTEM);
+      ModalWindow::OpenModalWindow(nullptr, ui::MODAL_TYPE_SYSTEM);
     } else if (sender == window_modal_button_) {
       ModalWindow::OpenModalWindow(GetWidget()->GetNativeView(),
                                    ui::MODAL_TYPE_WINDOW);