Helper function to resolving the size of a node.
function _resolveNodeSize(node) {
        var localItemSize = itemSize;
        if (getItemSize) {
            localItemSize = getItemSize(node.renderNode, size);
        }
        if ((localItemSize[0] === true) || (localItemSize[1] === true)) {
            var result = context.resolveSize(node, size);
            if (localItemSize[0] !== true) {
                result[0] = itemSize[0];
            }
            if (localItemSize[1] !== true) {
                result[1] = itemSize[1];
            }
            return result;
        }
        else {
            return localItemSize;
        }
    }