code: func (s *Service) Preupload(handlersendpointsv1digestcollection *HandlersEndpointsV1DigestCollection) *PreuploadCall {
  	c := &PreuploadCall{s: s, urlParams_: make(gensupport.URLParams)}
  	c.handlersendpointsv1digestcollection = handlersendpointsv1digestcollection
  	return c
  }
docs: // Preupload: Checks for entry's existence and generates upload URLs.
  // Arguments: request: the DigestCollection to be posted Returns: the
  // UrlCollection corresponding to the uploaded digests The response list
  // is commensurate to the request's; each UrlMessage has * if an entry
  // is missing: two URLs: the URL to upload a file to and the URL to call
  // when the upload is done (can be null). * if the entry is already
  // present: null URLs (''). UrlCollection([ UrlMessage( upload_url =
  // "<upload url>" finalize_url = "<finalize url>" ) UrlMessage(
  // upload_url = '') ... ])