On Yosemite, we can choose to hide the titlebar of the window and use the new unified look. However there is a rendering issue when using the unified look in full screen, and hiding the toolbar:
In the newWindow: method in DemoWindowController, add the following:
[[newWindowController window] setTitleVisibility:NSWindowTitleHidden];
[[newWindowController window] setCollectionBehavior:NSWindowCollectionBehaviorFullScreenPrimary];
Make the demo window full screen, and it looks ok:

Hide the toolbar (from the application menu or [Alt]+[Command]+T) and the tabs are no longer visible:
