mash: Fix crash when closing system tray menu

ash/common/wm/container_finder_unittest.cc

Index: ash/common/wm/container_finder_unittest.cc
diff --git a/ash/common/wm/container_finder_unittest.cc b/ash/common/wm/container_finder_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..cc814c368e1985b55796342de527a9b342f0fdc3
--- /dev/null
+++ b/ash/common/wm/container_finder_unittest.cc
@@ -0,0 +1,35 @@
+// Copyright 2016 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 "ash/common/wm/container_finder.h"
+
+#include <memory>
+
+#include "ash/common/shell_window_ids.h"
+#include "ash/common/wm_lookup.h"
+#include "ash/common/wm_window.h"
+#include "ash/test/ash_test_base.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ui/views/widget/widget.h"
+
+namespace ash {
+
+using ContainerFinderTest = test::AshTestBase;
+
+TEST_F(ContainerFinderTest, GetContainerForWindow) {
+  // Create a normal widget in the default container.
+  std::unique_ptr<views::Widget> widget = CreateTestWidget(
+      nullptr, kShellWindowId_DefaultContainer, gfx::Rect(1, 2, 3, 4));
+  WmWindow* window = WmLookup::Get()->GetWindowForWidget(widget.get());
+
+  // The window itself is not a container.
+  EXPECT_EQ(kShellWindowId_Invalid, window->GetShellWindowId());
+
+  // Container lookup finds the default container.
+  WmWindow* container = wm::GetContainerForWindow(window);
+  ASSERT_TRUE(container);
+  EXPECT_EQ(kShellWindowId_DefaultContainer, container->GetShellWindowId());
+}
+
+}  // namespace ash