code: private String addNewMethodToProto() {
      String methodName = METHOD_IN_PROTO_PREFIX + methodsInProtoCount;
      addMethodToProto(methodName);
      methodsInProtoCount++;
  
      return methodName;
    }
docs: Add a method to the ExposedType proto. This allows referencing them as this.__proto__.myMethod
  to pass them to Vue.js. This way of referencing works both in GWT2 and Closure. The method MUST
  have the @JsMethod annotation for this to work.