Save Changes? dialog may appear with wrong parent (DockDemoApp)

[andy-goryachev]

To reproduce:

• using DockDemoApp,
• open a number of windows some of which might present the Save Changes? dialog
• close the browser
  ---> the Save Changes? dialog should always appear parented to the window whose menu originated the action.

Example:

[andy-goryachev]

[andy-goryachev]