I use function from this Google API JS sample

```
function downloadFile(file, callback) {
  if (file.downloadUrl) {
    var accessToken = gapi.auth.getToken().access_token;
    var xhr = new XMLHttpRequest();
    xhr.open('GET', file.downloadUrl);
    xhr.setRequestHeader('Authorization', 'Bearer ' + accessToken);
    xhr.onload = function() {
      callback(xhr.responseText);
 };
 xhr.onerror = function() {
      callback(null);
 };
 xhr.send();
 } else {
    callback(null);
 }
}

```

I get file content, but how i can create Blob from xhr.responseText ?