Adds code for a new Aura shell.

ui/aura/layout_manager.h

+// Copyright (c) 2011 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 UI_AURA_LAYOUT_MANAGER_H_
+#define UI_AURA_LAYOUT_MANAGER_H_
+#pragma once
+
+namespace aura {
+
+// An interface implemented by an object that places child windows.
+class LayoutManager {
+ public:
+  virtual ~LayoutManager() {}
+
+  // Called when the window is resized.
+  virtual void OnWindowResized() = 0;
+};
+
+}  // namespace aura
+
+#endif  // UI_AURA_LAYOUT_MANAGER_H_