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

ui/views/mus/window_tree_host_mus.cc

 // 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.
 
 #include "ui/views/mus/window_tree_host_mus.h"
 
 #include "ui/aura/window.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/events/event.h"
 #include "ui/views/mus/input_method_mus.h"
 #include "ui/views/mus/native_widget_mus.h"
 #include "ui/views/mus/platform_window_mus.h"
 
 namespace views {
 
 ////////////////////////////////////////////////////////////////////////////////
 // WindowTreeHostMus, public:
 
-WindowTreeHostMus::WindowTreeHostMus(mojo::shell::mojom::Shell* shell,
+WindowTreeHostMus::WindowTreeHostMus(mojo::Shell* shell,
                                      NativeWidgetMus* native_widget,
                                      mus::Window* window)
     : native_widget_(native_widget),
       show_state_(ui::PLATFORM_WINDOW_STATE_UNKNOWN) {
   SetPlatformWindow(
       make_scoped_ptr(new PlatformWindowMus(this, shell, window)));
   // The location of events is already transformed, and there is no way to
   // correctly determine the reverse transform. So, don't attempt to transform
   // event locations, else the root location is wrong.
   // TODO(sky): we need to transform for device scale though.
@@ skipping 40 matching lines @@
   if (native_widget_)
     native_widget_->OnActivationChanged(active);
   WindowTreeHostPlatform::OnActivationChanged(active);
 }
 
 void WindowTreeHostMus::OnCloseRequest() {
   OnHostCloseRequested();
 }
 
 }  // namespace views