Implement a MusBrowserFrame.

ui/views/mus/window_tree_host_mus.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_VIEWS_MUS_WINDOW_TREE_HOST_MUS_H_
 #define UI_VIEWS_MUS_WINDOW_TREE_HOST_MUS_H_
 
 #include "base/macros.h"
 #include "components/mus/public/interfaces/window_tree.mojom.h"
 #include "ui/aura/window_tree_host_platform.h"
@@ skipping 17 matching lines @@
 class InputMethodMUS;
 class SurfaceContextFactory;
 
 class WindowTreeHostMus : public aura::WindowTreeHostPlatform {
  public:
   WindowTreeHostMus(mojo::Shell* shell,
                     mus::Window* window,
                     mus::mojom::SurfaceType surface_type);
   ~WindowTreeHostMus() override;
 
+  mus::Window* mus_window() { return mus_window_; }
+
   using WindowTreeHostPlatform::platform_window;
   ui::PlatformWindowState show_state() const { return show_state_; }
 
  private:
   // aura::WindowTreeHostPlatform:
   void OnClosed() override;
   void OnWindowStateChanged(ui::PlatformWindowState new_state) override;
   void OnActivationChanged(bool active) override;
 
   mus::Window* mus_window_;
   scoped_ptr<InputMethodMUS> input_method_;
   scoped_ptr<SurfaceContextFactory> context_factory_;
   ui::PlatformWindowState show_state_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeHostMus);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_MUS_WINDOW_TREE_HOST_MUS_H_