Bug 1436904 - Part 1: Add a static constructor function for display items. r=Bas

layout/forms/nsComboboxControlFrame.cpp

@@ -1599,7 +1599,7 @@ nsComboboxControlFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
            !presContext->GetTheme()->ThemeDrawsFocusForWidget(disp->mAppearance)) &&
           mDisplayFrame && IsVisibleForPainting(aBuilder)) {
         aLists.Content()->AppendToTop(
-          new (aBuilder) nsDisplayComboboxFocus(aBuilder, this));
+          MakeDisplayItem<nsDisplayComboboxFocus>(aBuilder, this));
       }
     }
   }