DelegateMethod methodName(String methodName) {
        this.methodName = Optional.of(methodName);
        return this;
      }
Parameter object to simplify the branches of {@link #format(CodeBlock, CodeBlock,
TypeMirror)} that call a delegate method.
value/src/main/java/com/google/auto/value/extension/toprettystring/processor/ToPrettyStringExtension.java