tiupload or the firebase-storage-ref
    *
    * For example:
    *
    *     <firebase-storage-upload-task
    *       task="[[task]]"
    *       bytes-transferred="{{bytesTransferred}}"
    *       total-bytes="{{totalBytes}}"
    *       state="{{state}}"
    *       download-url="{{downloadUrl}}"
    *       metadata="{{metadata}}"
    *       path="{{path}}"></firebase-storage-upload-task>
    *
    * It has to get the upload task from either the firebase-storage-multiupload or firebase-storage-ref
  