Failed attempt at automatically adjusting content surface

gistfile1.js

    // Constructor function for our ContentView class
    function ContentView() {
        // Applies View's constructor function to ContentView class
        View.apply(this, arguments);

        var content = TextData['mycontent'];

        // Backgrounds
        this.add(new Surface({
            size: [undefined, undefined],
            classes: ['black-bg']
        }));
        this.add(new StateModifier({
            origin: [0.5, 0.5]
        })).add(new Surface({
            size: [1024, undefined],
            classes: ['grey-bg']
        }));

        // Text
        this.contentSurface = new Surface({
            size: [500, this.getSize()[1]-100],  // <--- THIS FAILS
            classes: ['grey-bg', 'scrollable'],
            content: content,
            properties: {
                textAlign: 'center'
            }
        });

        // Center it in the content view
        var centerModifier = new StateModifier({
            origin: [0.5, 0.5],
            transform: Transform.translate(0, 100, 0)
        });
        this.add(centerModifier).add(this.contentSurface);
    }