Finishes the calculations on an axis. This basically just assigns the remaining
space to the center region.
@private
function (ownerContext, axis) {
        var size = axis.end - axis.begin,
            center = ownerContext.centerRegion;

        if (center) {
            center['set' + axis.sizePropCap](size - center.getMarginInfo()[axis.sizeProp]);
            center.layoutPos[axis.posProp] = axis.begin;
        }

        return Ext.isNumber(size) ? 1 : 0;
    }