views/mus: Fix some flaky crashes during test teardown.

ui/views/test/views_test_base.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/test/views_test_base.h"
 
 #include <utility>
 
 #include "base/run_loop.h"
 #include "ui/base/clipboard/clipboard.h"
@@ skipping 50 matching lines @@
   run_loop.RunUntilIdle();
 }
 
 Widget::InitParams ViewsTestBase::CreateParams(
     Widget::InitParams::Type type) {
   Widget::InitParams params(type);
   params.context = GetContext();
   return params;
 }
 
-void ViewsTestBase::DisableNativeWidgetMus() {
-  ViewsDelegate::GetInstance()->set_native_widget_factory(
-      ViewsDelegate::NativeWidgetFactory());
-}
-
 gfx::NativeWindow ViewsTestBase::GetContext() {
   return test_helper_->GetContext();
 }
 
 }  // namespace views