mash: Migrate shelf app list button to wm common types

ash/shelf/shelf_widget.cc

Index: ash/shelf/shelf_widget.cc
diff --git a/ash/shelf/shelf_widget.cc b/ash/shelf/shelf_widget.cc
index 44834c37ec7a274d92ef87393c81af9f204b6aba..d7f11bcdbb098f49c9b98fdd639ffb3d24df944b 100644
--- a/ash/shelf/shelf_widget.cc
+++ b/ash/shelf/shelf_widget.cc
@@ -726,9 +726,9 @@ bool ShelfWidget::GetDimsShelf() const {
 void ShelfWidget::CreateShelf(WmShelfAura* wm_shelf_aura) {
   DCHECK(!shelf_);
 
-  Shell* shell = Shell::GetInstance();
-  ShelfDelegate* delegate = shell->GetShelfDelegate();
-  shelf_.reset(new Shelf(shell->shelf_model(), delegate, wm_shelf_aura, this));
+  ShelfDelegate* delegate = Shell::GetInstance()->GetShelfDelegate();
+  shelf_.reset(
+      new Shelf(WmShell::Get()->shelf_model(), delegate, wm_shelf_aura, this));
   // Must be initialized before the delegate is notified because the delegate
   // may try to access the WmShelf.
   wm_shelf_aura->SetShelf(shelf_.get());