ash: Convert ShelfDelegate to use WmShelf* instead of Shelf*

ash/shell/shell_delegate_impl.h

Index: ash/shell/shell_delegate_impl.h
diff --git a/ash/shell/shell_delegate_impl.h b/ash/shell/shell_delegate_impl.h
index baf56f22ce7169d1921ec4d9b98723bfef181926..6edc418daa55b83080531636c13385e3fb984a2a 100644
--- a/ash/shell/shell_delegate_impl.h
+++ b/ash/shell/shell_delegate_impl.h
@@ -23,8 +23,6 @@ class KeyboardUI;
 namespace ash {
 namespace shell {
 
-class ShelfDelegateImpl;
-
 class ShellDelegateImpl : public ShellDelegate {
  public:
   ShellDelegateImpl();
@@ -57,7 +55,7 @@ class ShellDelegateImpl : public ShellDelegate {
   gfx::Image GetDeprecatedAcceleratorImage() const override;
 
  private:
-  ShelfDelegateImpl* shelf_delegate_;
+  ShelfDelegate* shelf_delegate_;
   std::unique_ptr<app_list::AppListPresenterDelegateFactory>
       app_list_presenter_delegate_factory_;
   std::unique_ptr<app_list::AppListPresenterImpl> app_list_presenter_;