function StreamHelper(worker, outputType, mimeType) {
    var internalType = outputType;
    switch(outputType) {
        case "blob":
        case "arraybuffer":
            internalType = "uint8array";
        break;
        case "base64":
            internalType = "string";
        break;
    }

    try {
        // the type used internally
        this._internalType = internalType;
        // the type used to output results
        this._outputType = outputType;
        // the mime type
        this._mimeType = mimeType;
        utils.checkSupport(internalType);
        this._worker = worker.pipe(new ConvertWorker(internalType));
        // the last workers can be rewired without issues but we need to
        // prevent any updates on previous workers.
        worker.lock();
    } catch(e) {
        this._worker = new GenericWorker("error");
        this._worker.error(e);
    }
}
An helper to easily use workers outside of JSZip.
@constructor
@param {Worker} worker the worker to wrap
@param {String} outputType the type of data expected by the use
@param {String} mimeType the mime type of the content, if applicable.