Move enum MenuAnchorPosition to reduce deps on menu_item_view.h

ash/root_window_controller.cc

Index: ash/root_window_controller.cc
diff --git a/ash/root_window_controller.cc b/ash/root_window_controller.cc
index 010ef0e3aee29217dd917aaae050649ebaf8558a..368dd92fe9c63a297b1257df7c1fce06c32ba7f8 100644
--- a/ash/root_window_controller.cc
+++ b/ash/root_window_controller.cc
@@ -569,9 +569,11 @@ void RootWindowController::ShowContextMenu(const gfx::Point& location_in_screen,
 
   views::MenuRunner menu_runner(menu_model.get());
   if (menu_runner.RunMenuAt(wallpaper_controller_->widget(),
-          NULL, gfx::Rect(location_in_screen, gfx::Size()),
-          views::MenuItemView::TOPLEFT, source_type,
-          views::MenuRunner::CONTEXT_MENU) ==
+                            NULL,
+                            gfx::Rect(location_in_screen, gfx::Size()),
+                            views::MENU_ANCHOR_TOPLEFT,
+                            source_type,
+                            views::MenuRunner::CONTEXT_MENU) ==
       views::MenuRunner::MENU_DELETED) {
     return;
   }