Add child for parent_mus when params.parent_mus is not initialized.

ash/mus/window_manager_ash_unittest.cc

Index: ash/mus/window_manager_ash_unittest.cc
diff --git a/ash/mus/window_manager_ash_unittest.cc b/ash/mus/window_manager_ash_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..bfc842995a6716d20a6dba0ef50ce0a8e8a61d12
--- /dev/null
+++ b/ash/mus/window_manager_ash_unittest.cc
@@ -0,0 +1,56 @@
+
+#include "ash/mus/test/wm_test_base.h"
+#include "base/macros.h"
+#include "base/bind.h"
+#include "services/ui/public/cpp/window.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ash/mus/root_window_controller.h"
+
+namespace ash {
+class WindowManagerAshTest : public mus::WmTestBase {
+ public:
+  WindowManagerAshTest() {}
+
+  void SetUp() override { mus::WmTestBase::SetUp(); }
+
+  ~WindowManagerAshTest() override {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(WindowManagerAshTest);
+};
+
+TEST_F(WindowManagerAshTest, isWidgetShownInCorrectDisplay) {
+  if (!SupportsMultipleDisplays())
+    return;
+
+  UpdateDisplay("400x400,500x500");
+
+  EXPECT_NE(GetPrimaryRootWindowController(),
+            GetSecondaryRootWindowController());
+  LOG(ERROR) << "\n\n GetPrimaryRootWindowController()->display().id() "
+             << GetPrimaryRootWindowController()->display().id();
+  LOG(ERROR) << "\n\n GetSecondaryRootWindowController()->display().id() "
+             << GetSecondaryRootWindowController()->display().id();
+
+  // ui::Window* ui_primary_window = CreateTestWindow(gfx::Rect(5, 5, 5, 5),
+  // ui::wm::TOP_LEVEL, GetPrimaryRootWindowController());
+  // ui::Window* ui_secondary_window = CreateTestWindow(gfx::Rect(10, 10, 20,
+  // 20), ui::wm::WINDOW_TYPE_NORMAL, GetSecondaryRootWindowController());
+
+  ui::Window* ui_primary_window =
+      CreateFullscreenTestWindow(GetPrimaryRootWindowController());
+  ui::Window* ui_secondary_window =
+      CreateFullscreenTestWindow(GetSecondaryRootWindowController());
+
+  EXPECT_NE(GetPrimaryRootWindowController(),
+            GetSecondaryRootWindowController());
+
+  DCHECK(ui_primary_window);
+  DCHECK(ui_secondary_window);
+
+  EXPECT_NE(ui_primary_window->display_id(), ui_secondary_window->display_id());
+  // LOG(ERROR) << "\n\n GetPrimaryRootWindow() " << GetPrimaryRootWindow();
+  // LOG(ERROR) << "\n\n GetPrimaryRootWindow() " << GetSecondaryRootWindow();
+}
+
+}  // namespace ash