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

components/mus/public/cpp/window_tree_host_factory.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 COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_HOST_FACTORY_H_
 #define COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_HOST_FACTORY_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "components/mus/public/interfaces/window_tree.mojom.h"
 #include "components/mus/public/interfaces/window_tree_host.mojom.h"
 #include "mojo/public/cpp/bindings/binding.h"
 
 namespace mojo {
-class ApplicationImpl;
+class Shell;
 }
 
 namespace mus {
 
 class WindowManagerDelegate;
 class WindowTreeDelegate;
 
 // The following create a new window tree host. Supply a |factory| if you have
-// already connected to mus, otherwise supply |app|, which contacts mus and
+// already connected to mus, otherwise supply |shell|, which contacts mus and
 // obtains a WindowTreeHostFactory.
 void CreateWindowTreeHost(mojom::WindowTreeHostFactory* factory,
                           WindowTreeDelegate* delegate,
                           mojom::WindowTreeHostPtr* host,
                           WindowManagerDelegate* window_manager_delegate);
-void CreateWindowTreeHost(mojo::ApplicationImpl* app,
+void CreateWindowTreeHost(mojo::Shell* shell,
                           WindowTreeDelegate* delegate,
                           mojom::WindowTreeHostPtr* host,
                           WindowManagerDelegate* window_manager_delegate);
 
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_HOST_FACTORY_H_