mustash: Enable connections to mus from the Chrome renderer [take 2]

ui/aura/mus/mus_util.h

+// 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 UI_AURA_MUS_MUS_UTIL_H_
+#define UI_AURA_MUS_MUS_UTIL_H_
+
+#include "ui/aura/aura_export.h"
+
+namespace mus {
+class Window;
+}
+
+namespace aura {
+
+class Window;
+
+AURA_EXPORT mus::Window* GetMusWindow(Window* window);
+
+AURA_EXPORT void SetMusWindow(Window* window, mus::Window* mus_window);
+
+}  // namespace aura
+
+#endif  // UI_AURA_MUS_MUS_UTIL_H_