Extract shell methods from ApplicationImpl into a base class, and pass this to Initialize() instead.

components/mus/public/cpp/lib/window_tree_client_impl.h

 // Copyright 2014 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 COMPONENTS_MUS_PUBLIC_CPP_LIB_WINDOW_TREE_CLIENT_IMPL_H_
 #define COMPONENTS_MUS_PUBLIC_CPP_LIB_WINDOW_TREE_CLIENT_IMPL_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 27 matching lines @@
                              public mojom::WindowTreeClient,
                              public mojom::WindowManager,
                              public WindowManagerClient {
  public:
   WindowTreeClientImpl(WindowTreeDelegate* delegate,
                        WindowManagerDelegate* window_manager_delegate,
                        mojo::InterfaceRequest<mojom::WindowTreeClient> request);
   ~WindowTreeClientImpl() override;
 
   // Establishes the connection by way of the WindowTreeFactory.
-  void ConnectViaWindowTreeFactory(mojo::ApplicationImpl* app);
+  void ConnectViaWindowTreeFactory(mojo::Shell* shell);
 
   // Wait for OnEmbed(), returning when done.
   void WaitForEmbed();
 
   bool connected() const { return tree_ != nullptr; }
   ConnectionSpecificId connection_id() const { return connection_id_; }
 
   // API exposed to the window implementations that pushes local changes to the
   // service.
   void DestroyWindow(Window* window);
@@ skipping 223 matching lines @@
   scoped_ptr<mojo::AssociatedBinding<mojom::WindowManager>>
       window_manager_internal_;
   mojom::WindowManagerClientAssociatedPtr window_manager_internal_client_;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(WindowTreeClientImpl);
 };
 
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_PUBLIC_CPP_LIB_WINDOW_TREE_CLIENT_IMPL_H_