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

components/mus/ws/window_tree_host_impl.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 "components/mus/ws/window_tree_host_impl.h"
 
 #include "base/debug/debugger.h"
 #include "base/strings/utf_string_conversions.h"
 #include "components/mus/common/types.h"
 #include "components/mus/public/interfaces/input_event_constants.mojom.h"
@@ skipping 69 matching lines @@
   const bool in_nonclient_area_;
 
   DISALLOW_COPY_AND_ASSIGN(ProcessedEventTarget);
 };
 
 WindowTreeHostImpl::QueuedEvent::QueuedEvent() {}
 WindowTreeHostImpl::QueuedEvent::~QueuedEvent() {}
 
 WindowTreeHostImpl::WindowTreeHostImpl(
     ConnectionManager* connection_manager,
-    mojo::ApplicationImpl* app_impl,
+    mojo::Shell* shell,
     const scoped_refptr<GpuState>& gpu_state,
     const scoped_refptr<SurfacesState>& surfaces_state)
     : id_(next_id++),
       delegate_(nullptr),
       connection_manager_(connection_manager),
       event_dispatcher_(this),
       display_manager_(
-          DisplayManager::Create(app_impl, gpu_state, surfaces_state)),
+          DisplayManager::Create(shell, gpu_state, surfaces_state)),
       tree_awaiting_input_ack_(nullptr),
       last_cursor_(0) {
   frame_decoration_values_ = mojom::FrameDecorationValues::New();
   frame_decoration_values_->normal_client_area_insets = mojo::Insets::New();
   frame_decoration_values_->maximized_client_area_insets = mojo::Insets::New();
   frame_decoration_values_->max_title_bar_button_width = 0u;
 
   display_manager_->Init(this);
 }
 
@@ skipping 378 matching lines @@
   DispatchInputEventToWindowImpl(target, in_nonclient_area, std::move(event));
 }
 
 void WindowTreeHostImpl::OnWindowDestroyed(ServerWindow* window) {
   windows_needing_frame_destruction_.erase(window);
   window->RemoveObserver(this);
 }
 
 }  // namespace ws
 }  // namespace mus