How to upload files in Web Workers without using FormData

How can I retrieve $_FILES in PHP when I upload through a Web Worker? When I tried to use FormData, I got the following error:

Error: FormData is not defined

This is my code:

function uploadFile(blobFile, fileName, filePart, totalChunks) {
    //if I try to put this
    //var formData = new FormData(); //it does not work
    var xhr = new XMLHttpRequest();                
    xhr.open("POST", "upload.php"+"?"+"file="+fileName + filePart, true);
    xhr.onload = function(e) {};
    xhr.send(blobFile);
}   

So in upload.php how am I supposed to get the tmp path from $_FILES ? Just in case, I will also show the page referencing the Web worker:

<form id="fileuploader" enctype="multipart/form-data" method="post" action="upload.php">
    <label for="fileToUpload">Select Files to Upload</label><br />
    <input type="file" name="fileToUpload[]" multiple="" id="fileToUpload" onchange="fileList();"/><br />
    <input type="button" onclick="sendRequest();" value="Upload" />
    <!-- a place for File Listing -->
    <div id="fileList"></div>           
</form>
<script type="text/javascript">
function sendRequest() {
    var worker = new Worker("fileupload.js");
    worker.onmessage = function(e) {
        alert(e.data);
    }
    var file = document.getElementById('fileToUpload');
    for(var i = 0; i < file.files.length; i++) { 
        worker.postMessage(file.files[i]);  
    }
}