Make GetRootWindow() return a Window instead of a RootWindow.

ash/shelf/shelf_alignment_menu.h

Index: ash/shelf/shelf_alignment_menu.h
diff --git a/ash/shelf/shelf_alignment_menu.h b/ash/shelf/shelf_alignment_menu.h
index 288de9aa23b2ec478be6d24b86d797e2424ebcd3..e7acce2831527b86d73f486396e18eb97b5c1d7a 100644
--- a/ash/shelf/shelf_alignment_menu.h
+++ b/ash/shelf/shelf_alignment_menu.h
@@ -19,7 +19,7 @@ namespace ash {
 class ASH_EXPORT ShelfAlignmentMenu : public ui::SimpleMenuModel,
                                       public ui::SimpleMenuModel::Delegate {
  public:
-  explicit ShelfAlignmentMenu(aura::RootWindow* root);
+  explicit ShelfAlignmentMenu(aura::Window* root);
   virtual ~ShelfAlignmentMenu();
 
   // ui::SimpleMenuModel::Delegate overrides:
@@ -38,7 +38,7 @@ class ASH_EXPORT ShelfAlignmentMenu : public ui::SimpleMenuModel,
     MENU_ALIGN_BOTTOM,
   };
 
-  aura::RootWindow* root_window_;
+  aura::Window* root_window_;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfAlignmentMenu);
 };