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

ash/aura/wm_root_window_controller_aura.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/aura/wm_root_window_controller_aura.h"
 
 #include "ash/aura/wm_shelf_aura.h"
 #include "ash/aura/wm_shell_aura.h"
 #include "ash/aura/wm_window_aura.h"
 #include "ash/common/shelf/shelf_widget.h"
@@ skipping 49 matching lines @@
       root_window_controller->GetRootWindow()->GetProperty(
           kWmRootWindowControllerKey);
   if (wm_root_window_controller)
     return wm_root_window_controller;
 
   // WmRootWindowControllerAura is owned by the RootWindowController's window.
   return new WmRootWindowControllerAura(root_window_controller);
 }
 
 bool WmRootWindowControllerAura::HasShelf() {
-  return root_window_controller_->shelf_widget() != nullptr;
+  return root_window_controller_->wm_shelf_aura()->shelf_widget() != nullptr;
 }
 
 WmShell* WmRootWindowControllerAura::GetShell() {
   return WmShell::Get();
 }
 
 AlwaysOnTopController* WmRootWindowControllerAura::GetAlwaysOnTopController() {
   return root_window_controller_->always_on_top_controller();
 }
 
@@ skipping 50 matching lines @@
     const display::Display& display) {}
 
 void WmRootWindowControllerAura::OnDisplayMetricsChanged(
     const display::Display& display,
     uint32_t metrics) {
   FOR_EACH_OBSERVER(WmRootWindowControllerObserver, *observers(),
                     OnWorkAreaChanged());
 }
 
 }  // namespace ash