class LayoutTestVC: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let testView = YourCustomView(frame: .init(x: 0, y: 0, width: 300, height: 160))
    }

}

class ContentView: UIView {
}

class YourCustomView: UIView {

    var contentView: ContentView!
    let thumbWidth: CGFloat = 40.0

    override init(frame: CGRect) {
        super.init(frame: frame)
        setupContentView()
    }
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        setupContentView()
    }

    private func setupContentView() {
        contentView = ContentView(frame: .zero)
        contentView.translatesAutoresizingMaskIntoConstraints = false
        addSubview(contentView)
        contentView.leftAnchor.constraint(equalTo: leftAnchor, constant:thumbWidth).isActive = true
        contentView.rightAnchor.constraint(equalTo: rightAnchor, constant: -thumbWidth).isActive = true
        contentView.topAnchor.constraint(equalTo: topAnchor).isActive = true
        contentView.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
        contentView.clipsToBounds = true
        contentView.isUserInteractionEnabled = true
        contentView.layoutIfNeeded()
        NSLog("ContentView bounds \(contentView.bounds), view bounds \(self.bounds)")
    }

}