ui: Cleanup class/struct forward declarations

ash/common/shelf/shelf_view.cc

Index: ash/common/shelf/shelf_view.cc
diff --git a/ash/common/shelf/shelf_view.cc b/ash/common/shelf/shelf_view.cc
index a54444a4eacee55dc5d6526a4a6d963777882c2c..1ef382414359a6b63709161ea25c47b398072c91 100644
--- a/ash/common/shelf/shelf_view.cc
+++ b/ash/common/shelf/shelf_view.cc
@@ -1060,7 +1060,7 @@ void ShelfView::AnimateToIdealBounds() {
     // Now that the item animation starts, we have to make sure that the
     // padding of the first gets properly transferred to the new first item.
     if (i && view->border())
-      view->SetBorder(views::Border::NullBorder());
+      view->SetBorder(views::NullBorder());
   }
   overflow_button_->SetBoundsRect(ideal_bounds.overflow_bounds);
 }