mash: Move WmShelfAura ownership to RootWindowController and init it earlier

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/wm_root_window_controller_observer.h"
@@ skipping 60 matching lines @@
 
 wm::WorkspaceWindowState WmRootWindowControllerAura::GetWorkspaceWindowState() {
   return root_window_controller_->workspace_controller()->GetWindowState();
 }
 
 AlwaysOnTopController* WmRootWindowControllerAura::GetAlwaysOnTopController() {
   return root_window_controller_->always_on_top_controller();
 }
 
 WmShelf* WmRootWindowControllerAura::GetShelf() {
-  return root_window_controller_->shelf_widget()
-             ? root_window_controller_->shelf_widget()->shelf()->wm_shelf()
-             : nullptr;
+  return root_window_controller_->wm_shelf_aura();
 }
 
 WmWindow* WmRootWindowControllerAura::GetWindow() {
   return WmWindowAura::Get(root_window_controller_->GetRootWindow());
 }
 
 void WmRootWindowControllerAura::ConfigureWidgetInitParamsForContainer(
     views::Widget* widget,
     int shell_container_id,
     views::Widget::InitParams* init_params) {
@@ skipping 43 matching lines @@
 void WmRootWindowControllerAura::OnShelfAlignmentChanged(
     aura::Window* root_window) {
   if (root_window != root_window_controller_->GetRootWindow())
     return;
 
   FOR_EACH_OBSERVER(WmRootWindowControllerObserver, observers_,
                     OnShelfAlignmentChanged());
 }
 
 }  // namespace ash