@Override
  public UnaryCallable<GetRuntimeVersionRequest, RuntimeVersion> getRuntimeVersionCallable() {
    return getRuntimeVersionCallable;
  }
Constructs an instance of HttpJsonTpuStub, using the given settings. This is protected so that
it is easy to make a subclass, but otherwise, the static factory methods should be preferred.
java-tpu/google-cloud-tpu/src/main/java/com/google/cloud/tpu/v2/stub/HttpJsonTpuStub.java