@Override
  public IncrementalExtensionType incrementalType(ProcessingEnvironment processingEnvironment) {
    return IncrementalExtensionType.ISOLATING;
  }
An extension that implements the {@link com.google.auto.value.extension.memoized.Memoized}
contract.
value/src/main/java/com/google/auto/value/extension/memoized/processor/MemoizeExtension.java