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

ash/common/shelf/shelf_widget.cc

Index: ash/common/shelf/shelf_widget.cc
diff --git a/ash/common/shelf/shelf_widget.cc b/ash/common/shelf/shelf_widget.cc
index 4d6a79089a3f2fab8abc3d692b5bbb33e140e202..01d4109f45bb570eaff9a4f9d83a8a2400229ad1 100644
--- a/ash/common/shelf/shelf_widget.cc
+++ b/ash/common/shelf/shelf_widget.cc
@@ -287,10 +287,9 @@ void ShelfWidget::DelegateView::UpdateShelfAssetBackground(int alpha) {
   SchedulePaint();
 }
 
-ShelfWidget::ShelfWidget(WmWindow* shelf_container,
-                         WmWindow* status_container,
-                         WmShelf* wm_shelf)
+ShelfWidget::ShelfWidget(WmWindow* shelf_container, WmShelf* wm_shelf)
     : wm_shelf_(wm_shelf),
+      status_area_widget_(nullptr),
       delegate_view_(new DelegateView(wm_shelf, this)),
       shelf_view_(nullptr),
       background_animator_(SHELF_BACKGROUND_DEFAULT, wm_shelf_),
@@ -320,17 +319,6 @@ ShelfWidget::ShelfWidget(WmWindow* shelf_container,
   background_animator_.PaintBackground(
       shelf_layout_manager_->GetShelfBackgroundType(),
       BACKGROUND_CHANGE_IMMEDIATE);
-  wm_shelf_->SetShelfLayoutManager(shelf_layout_manager_);
-
-  // TODO(jamescook): Move ownership to RootWindowController.
-  status_area_widget_ = new StatusAreaWidget(status_container, wm_shelf_);
-  status_area_widget_->CreateTrayViews();
-  if (WmShell::Get()->GetSessionStateDelegate()->IsActiveUserSessionStarted())
-    status_area_widget_->Show();
-  WmShell::Get()->focus_cycler()->AddWidget(status_area_widget_);
-  background_animator_.AddObserver(status_area_widget_);
-  status_container->SetLayoutManager(
-      base::MakeUnique<StatusAreaLayoutManager>(this));
 
   views::Widget::AddObserver(this);
 }
@@ -345,6 +333,20 @@ ShelfWidget::~ShelfWidget() {
   background_animator_.RemoveObserver(this);
 }
 
+void ShelfWidget::CreateStatusAreaWidget(WmWindow* status_container) {
+  DCHECK(status_container);
+  DCHECK(!status_area_widget_);
+  // TODO(jamescook): Move ownership to RootWindowController.
+  status_area_widget_ = new StatusAreaWidget(status_container, wm_shelf_);
+  status_area_widget_->CreateTrayViews();
+  if (WmShell::Get()->GetSessionStateDelegate()->IsActiveUserSessionStarted())
+    status_area_widget_->Show();
+  WmShell::Get()->focus_cycler()->AddWidget(status_area_widget_);
+  background_animator_.AddObserver(status_area_widget_);
+  status_container->SetLayoutManager(
+      base::MakeUnique<StatusAreaLayoutManager>(this));
+}
+
 void ShelfWidget::SetPaintsBackground(
     ShelfBackgroundType background_type,
     BackgroundAnimatorChangeType change_type) {