code: func (dr *DescribeRequest) blobInitiallyRequested(br blob.Ref) bool {
  	if dr.BlobRef.Valid() && dr.BlobRef == br {
  		return true
  	}
  	for _, br1 := range dr.BlobRefs {
  		if br == br1 {
  			return true
  		}
  	}
  	return false
  }
docs: // Requires dr.mu is held.