ash: Move ShelfWidget ownership to WmShelf and refactor access to it

ash/mus/root_window_controller.cc

 // Copyright 2016 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 "ash/mus/root_window_controller.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 #include <map>
@@ skipping 152 matching lines @@
 }
 
 void RootWindowController::CreateLayoutManagers() {
   // Override the default layout managers for certain containers.
   WmWindowMus* lock_screen_container =
       GetWindowByShellWindowId(kShellWindowId_LockScreenContainer);
   layout_managers_[lock_screen_container->mus_window()].reset(
       new ScreenlockLayout(lock_screen_container->mus_window()));
 
   // Creating the shelf also creates the status area and both layout managers.
-  wm_shelf_.reset(new WmShelfMus(wm_root_window_controller_.get()));
+  wm_shelf_.reset(new WmShelfMus(wm_root_window_controller_->GetWindow()));
 
   WmWindowMus* default_container =
       GetWindowByShellWindowId(kShellWindowId_DefaultContainer);
   // WorkspaceLayoutManager is not a mash::wm::LayoutManager (it's a
   // wm::LayoutManager), so it can't be in |layout_managers_|.
   workspace_layout_manager_ = new WorkspaceLayoutManager(default_container);
   default_container->SetLayoutManager(
       base::WrapUnique(workspace_layout_manager_));
 
   WmWindowMus* docked_container =
       GetWindowByShellWindowId(kShellWindowId_DockedContainer);
   std::unique_ptr<DockedWindowLayoutManager> docked_window_layout_manager =
       base::MakeUnique<DockedWindowLayoutManager>(docked_container);
   docked_window_layout_manager->SetShelf(wm_shelf_.get());
   docked_window_layout_manager->AddObserver(wm_shelf_->shelf_layout_manager());
   docked_container->SetLayoutManager(std::move(docked_window_layout_manager));
 
   WmWindowMus* panel_container =
       GetWindowByShellWindowId(kShellWindowId_PanelContainer);
   std::unique_ptr<PanelLayoutManager> panel_layout_manager =
       base::MakeUnique<PanelLayoutManager>(panel_container);
   panel_layout_manager->SetShelf(wm_shelf_.get());
   panel_container->SetLayoutManager(std::move(panel_layout_manager));
 }
 
 }  // namespace mus
 }  // namespace ash