code: public Crossfader withStructure(View first, int firstWidth, View second, int secondWidth) {
          withFirst(first, firstWidth);
          withSecond(second, secondWidth);
          return this;
      }
docs: define the default view and the slided view of the crossfader
  
  @param first
  @param firstWidth
  @param second
  @param secondWidth
  @return