Add rudimentary mash shelf functionality.

mash/wm/user_window_controller_impl.h

Index: mash/wm/user_window_controller_impl.h
diff --git a/mash/wm/user_window_controller_impl.h b/mash/wm/user_window_controller_impl.h
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+// Copyright 2015 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_USER_WINDOW_CONTROLLER_IMPL_H_
+#define MASH_WM_USER_WINDOW_CONTROLLER_IMPL_H_
+
+#include <stdint.h>
+
+#include "base/macros.h"
+#include "components/mus/common/types.h"
+#include "components/mus/public/cpp/window_observer.h"
+#include "mash/wm/public/interfaces/user_window_controller.mojom.h"
+
+namespace mash {
+namespace wm {
+
+class WindowManagerApplication;
+
+class UserWindowControllerImpl : public mash::wm::mojom::UserWindowController,
+                                 public mus::WindowObserver {
+ public:
+  UserWindowControllerImpl();
+  ~UserWindowControllerImpl() override;
+
+  void Initialize(WindowManagerApplication* state);
+
+ private:
+  // A helper to get the container for user windows.
+  mus::Window* GetUserWindowContainer() const;
+
+  // mus::WindowObserver:
+  void OnTreeChanging(const TreeChangeParams& params) override;
+
+  // mash::wm::mojom::UserWindowController:
+  void AddUserWindowObserver(
+      mash::wm::mojom::UserWindowObserverPtr observer) override;
+  void FocusUserWindow(uint32_t window_id) override;
+
+  WindowManagerApplication* state_;
+  mash::wm::mojom::UserWindowObserverPtr user_window_observer_;
+
+  DISALLOW_COPY_AND_ASSIGN(UserWindowControllerImpl);
+};
+
+}  // namespace wm
+}  // namespace mash
+
+#endif  // MASH_WM_USER_WINDOW_CONTROLLER_IMPL_H_