code: func WriteFileFromReader(ctx context.Context, bs blobserver.StatReceiver, filename string, r io.Reader) (blob.Ref, error) {
  	return WriteFileFromReaderWithModTime(ctx, bs, filename, time.Time{}, r)
  }
docs: // WriteFileFromReader creates and uploads a "file" JSON schema
  // composed of chunks of r, also uploading the chunks.  The returned
  // BlobRef is of the JSON file schema blob.
  // The filename is optional.