constructor (name, source, data)
    {
        this.name = name;
        this.source = source;
        this.data = data;
    }
@param {string} name Name of the file.
@param {FileSource} source Source of the file.
@param {string|File} data If the file source is url, this must be the url string. If the file source
is file, this must be a {@link File} object.