code: public void setUploadChunkSize(int chunkSize) {
      Preconditions.checkArgument(chunkSize > 0, "Upload chunk size must be great than 0.");
      Preconditions.checkArgument(
          chunkSize % MediaHttpUploader.MINIMUM_CHUNK_SIZE == 0,
          "Upload chunk size must be a multiple of MediaHttpUploader.MINIMUM_CHUNK_SIZE");
      if ((chunkSize > GCS_UPLOAD_GRANULARITY) && (chunkSize % GCS_UPLOAD_GRANULARITY != 0)) {
        logger.atWarning().log(
            "Upload chunk size should be a multiple of %s for best performance, got %s",
            GCS_UPLOAD_GRANULARITY, chunkSize);
      }
      uploadChunkSize = chunkSize;
    }
docs: Sets size of upload buffer used.