mash: remove more shell/shelf WmWindow usage.

ash/first_run/first_run_helper_impl.cc

Index: ash/first_run/first_run_helper_impl.cc
diff --git a/ash/first_run/first_run_helper_impl.cc b/ash/first_run/first_run_helper_impl.cc
index 6acfb9ef1897621fb0a4aa95dec18ce0298f13e5..2f39a62cc846c7e9b66c626d281dfeb0309b1bc2 100644
--- a/ash/first_run/first_run_helper_impl.cc
+++ b/ash/first_run/first_run_helper_impl.cc
@@ -56,7 +56,7 @@ views::Widget* FirstRunHelperImpl::GetOverlayWidget() {
 }
 
 gfx::Rect FirstRunHelperImpl::GetAppListButtonBounds() {
-  WmShelf* shelf = WmShelf::ForWindow(ShellPort::Get()->GetPrimaryRootWindow());
+  WmShelf* shelf = WmShelf::ForWindow(Shell::GetPrimaryRootWindow());
   AppListButton* app_button = shelf->shelf_widget()->GetAppListButton();
   return app_button->GetBoundsInScreen();
 }