[PATCH 0/1] MR9301: winemac.drv: Explicitly track the shape layer used for letter/pillarboxes.

[Tim Clem (＠tclem)]

The content view's layer can have internal sublayers from Cocoa, so
assuming anything about the hierarchy is dangerous and can result in
us removing backing layers for visible content.

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Fixes solid grey fullscreen windows in some games. It's not clear to me why the content view layer only sometimes has sublayers; it may be a macOS version difference or something, but either way we should not assume anything about what's going on in there.