mash/wm: Fix detecting container windows.

mash/wm/disconnected_app_handler.h

+// 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.
+
+#ifndef MASH_WM_DISCONNECTED_APP_HANDLER_H_
+#define MASH_WM_DISCONNECTED_APP_HANDLER_H_
+
+#include "base/macros.h"
+#include "components/mus/public/cpp/window_tracker.h"
+
+namespace mash {
+namespace wm {
+
+// Tracks mus::Windows for when they get disconnected from the embedded app.
+// Currently closes a window upon disconnection.
+class DisconnectedAppHandler : public mus::WindowTracker {
+ public:
+  DisconnectedAppHandler();
+  ~DisconnectedAppHandler() override;
+
+ private:
+  // mus::WindowObserver:
+  void OnWindowEmbeddedAppDisconnected(mus::Window* window) override;
+
+  DISALLOW_COPY_AND_ASSIGN(DisconnectedAppHandler);
+};
+
+}  // namespace wm
+}  // namespace mash
+
+#endif  // MASH_WM_DISCONNECTED_APP_HANDLER_H_