WidgetDelegateView is its own contents view.

ash/common/accelerators/exit_warning_handler.cc

 // Copyright 2013 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 "ash/common/accelerators/exit_warning_handler.h"
 
 #include "ash/common/shell_delegate.h"
 #include "ash/common/shell_window_ids.h"
 #include "ash/common/wm_root_window_controller.h"
 #include "ash/common/wm_shell.h"
@@ skipping 148 matching lines @@
   params.accept_events = false;
   params.keep_on_top = true;
   params.remove_standard_frame = true;
   params.delegate = delegate;
   params.bounds = bounds;
   params.name = "ExitWarningWindow";
   widget_.reset(new views::Widget);
   root_window->GetRootWindowController()->ConfigureWidgetInitParamsForContainer(
       widget_.get(), kShellWindowId_SettingBubbleContainer, &params);
   widget_->Init(params);
-  widget_->SetContentsView(delegate);
   widget_->Show();
 
   delegate->NotifyAccessibilityEvent(ui::AX_EVENT_ALERT, true);
 }
 
 void ExitWarningHandler::Hide() {
   widget_.reset();
 }
 
 }  // namespace ash