Ponerle sombra a un linear

public class LinearLayoutWithShadow extends LinearLayout {
    private Shadow shadow;
    public LinearLayoutWithShadow(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(attrs);
    }
    public LinearLayoutWithShadow(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(attrs);
    }
    protected void init(AttributeSet attrs) {
        setLayerType(LAYER_TYPE_SOFTWARE, null);
        shadow = new Shadow();
        shadow.init(this, attrs);
    }
    @Override public void draw(Canvas canvas) {
        shadow.draw(canvas);
        super.draw(canvas);
    }
}