code: func (u *ConcurrentUploader) UploadFile(item *Item, ps *isolatedclient.PushState, done func()) {
  	u.wg.Add(1)
  	go u.upload(item.RelPath, fileSource(item.Path), ps, done)
  }
docs: // UploadFile uploads a file from disk. UploadFile does not block. If
  // not-nil, the done func will be invoked on upload completion (both success
  // and failure).
  // TODO(djd): Consider using Upload directly and deleting UploadFile.