https://github.com/GoogleCloudPlatform/google-cloud-java/blob/master/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/spi/v1/Publisher.java#L183

addCallback is no longer available on ApiFuture, it is now a static method in ApiFutures.