code: public PubsubFuture<List<String>> publish(final String project, final String topic,
                                              final List<Message> messages) {
      return publish0(messages, Topic.canonicalTopic(project, topic));
    }
docs: Publish a batch of messages.
  
  @param project  The Google Cloud project.
  @param topic    The topic to publish on.
  @param messages The batch of messages.
  @return a future that is completed with a list of message ID's for the published messages.