code: public RecordTypeBuilder addProperty(String name, JSType type, Node propertyNode) {
      isEmpty = false;
      properties.put(name, new RecordProperty(type, propertyNode));
      return this;
    }
docs: Adds a property with the given name and type to the record type.
  If you add a property that has already been added, then {@link #build}
  will fail.
  
  @param name the name of the new property
  @param type the JSType of the new property
  @param propertyNode the node that holds this property definition
  @return The builder itself for chaining purposes.