WidgetDelegateView is its own contents view.

ui/views/widget/widget_delegate.cc

Index: ui/views/widget/widget_delegate.cc
diff --git a/ui/views/widget/widget_delegate.cc b/ui/views/widget/widget_delegate.cc
index 50dddcac0d63bcd3dc19e43d7d8d85ac0c898a0d..917124976c4a1505e9fdc6ce9ec4f9c8b5b802e6 100644
--- a/ui/views/widget/widget_delegate.cc
+++ b/ui/views/widget/widget_delegate.cc
@@ -204,6 +204,10 @@ const Widget* WidgetDelegateView::GetWidget() const {
   return View::GetWidget();
 }
 
+views::View* WidgetDelegateView::GetContentsView() {
+  return this;
+}
+
 const char* WidgetDelegateView::GetClassName() const {
   return kViewClassName;
 }