MacViews: Support ui::MODAL_TYPE_WINDOW with a null parent window.

components/constrained_window/constrained_window_views.h

 // 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.
 
 #ifndef COMPONENTS_CONSTRAINED_WINDOW_CONSTRAINED_WINDOW_VIEWS_H_
 #define COMPONENTS_CONSTRAINED_WINDOW_CONSTRAINED_WINDOW_VIEWS_H_
 
 #include <memory>
 
 #include "ui/gfx/native_widget_types.h"
@@ skipping 55 matching lines @@
     content::WebContents* initiator_web_contents);
 #endif
 
 // Create a widget for |dialog| that is modal to |web_contents|.
 // The modal type of |dialog->GetModalType()| must be ui::MODAL_TYPE_CHILD.
 views::Widget* CreateWebModalDialogViews(views::WidgetDelegate* dialog,
                                          content::WebContents* web_contents);
 
 // Create a widget for |dialog| that has a modality given by
 // |dialog->GetModalType()|.  The modal type must be either
-// ui::MODAL_TYPE_SYSTEM or ui::MODAL_TYPE_WINDOW.  This places the
-// dialog appropriately if |parent| is a valid browser window.
+// ui::MODAL_TYPE_SYSTEM or ui::MODAL_TYPE_WINDOW.  This places the dialog
+// appropriately if |parent| is a valid browser window. Currently, |parent| may
+// be null for MODAL_TYPE_WINDOW, but that's a bug and callers shouldn't rely on
+// that working. See http://crbug.com/657293.
 views::Widget* CreateBrowserModalDialogViews(views::DialogDelegate* dialog,
                                              gfx::NativeWindow parent);
 
 }  // namespace constrained_window
 
 #endif  // COMPONENTS_CONSTRAINED_WINDOW_CONSTRAINED_WINDOW_VIEWS_H_