var Metadata = {
  'title': fileData.fileName,'mimeType': contentType,'parents':["0B6NmmF3ovpsbExuOEc1R2JzSFEp"] // It is one of my folder's id.
};

var base64Data = btoa(reader.result);
var multipartRequestBody =
    delimiter +
    'Content-Type: application/json\r\n\r\n' +
    JSON.stringify(Metadata) +
    delimiter +
    'Content-Type: ' + contentType + '\r\n' +
    'Content-Transfer-Encoding: base64\r\n' +
    '\r\n' +
    base64Data +
    close_delim;

var request = gapi.client.request({
    'path': '/upload/drive/v2/files','method': 'POST','params': {'uploadType': 'multipart'},'headers': {
      'Content-Type': 'multipart/mixed; boundary="' + boundary + '"'
    },'body': multipartRequestBody});

 request.execute(callback);