Add simplistic screenlock application.

mash/wm/screenlock_layout.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_SCREENLOCK_LAYOUT_H_
+#define MASH_WM_SCREENLOCK_LAYOUT_H_
+
+#include "base/macros.h"
+#include "mash/wm/layout_manager.h"
+
+namespace mash {
+namespace wm {
+
+// Lays out the shelf within shelf containers.
+class ScreenlockLayout : public LayoutManager {
+ public:
+  explicit ScreenlockLayout(mus::Window* owner);
+  ~ScreenlockLayout() override;
+
+ private:
+  // Overridden from LayoutManager:
+  void LayoutWindow(mus::Window* window) override;
+
+  DISALLOW_COPY_AND_ASSIGN(ScreenlockLayout);
+};
+
+}  // namespace wm
+}  // namespace mash
+
+#endif  // MASH_WM_SCREENLOCK_LAYOUT_H_