What is the correct way to use the Vibrant Dark (`NSAppearanceNameVibrantDark`) or Vibrant Light (`NSAppearanceNameVibrantLight`) modes with an `NSWindow`? 

I'm building an application and would like to offer the new Vibrant Dark appearance as an option for the main application's `NSWindow`. The window itself is a pretty straight forward window with an `NSToolbar` across the top and a scroll view as the main content area. 

There's plenty of information from Apple on using the new vibrancy appearances in conjunction with an `NSVisualEffectsView`, but I'm looking for clarification on how to use those appearances on an `NSWindow`. 

In the `NSAppearance.h` header file, there's a comment that states that the vibrant appearances should only be set on an `NSVisualEffectsView`. There's no mention of it being supported on `NSWindow`.

The WWDC videos talk about making sure that you're using layer-backed views and that you're allowing vibrancy on your subviews when using the new vibrant appearances, but again, no mention of using them on an `NSWindow`. 

The VisualEffectsPlayground sample code does have an example of a Facetime-like application that uses the dark vibrancy mode, but it doesn't have a toolbar and it uses the full-content mask. 

From that information, I'm doing the following in my `NSWindowController's windowDidLoad` method: 

```
[self.window.contentView setWantsLayer:YES];
self.window.appearance = [NSAppearance appearanceNamed:NSAppearanceNameVibrantDark];

```

And, sure enough, I get a black `NSToolbar` with a black window title bar. So it *looks* like it's working properly, but when my scrollview scrolls its content (thumbnails of images) the standard translucency under the `NSToolbar` and the window's title bar is either not present or is randomly present. There doesn't seem to be any pattern. Sometimes when I scroll the scrollview, the content is shown in the "blurred" state under the toolbar and title bar. Other times when I scroll, the toolbar and titlebar are just an opaque black. (The title bar and toolbar still draw their titles and buttons.)

When I don't request a layer for the window's content view, then I get more a gray titlebar and window title rather than a "pure" black one. (My scrollview's background color can be either white, dark gray or black.)

Any help or clarification on how to properly configure an `NSWindow` (that contains an `NSToolbar` and an `NSScollView`) to use the new vibrancy appearances would be much appreciated.