The area inside the window that is for non-obscured content, in window coordinates.
Typically, the area represented by this property is the same as the frame of the contentView. However, for windows with NSFullSizeContentViewWindowMask set, there needs to be a way to determine the portion that is not under the toolbar. The contentLayoutRect property contains the portion of the layout that is not obscured under the toolbar. This property is KVO compliant.