code: public AutofitHelper addOnTextSizeChangeListener(OnTextSizeChangeListener listener) {
          if (mListeners == null) {
              mListeners = new ArrayList<OnTextSizeChangeListener>();
          }
          mListeners.add(listener);
          return this;
      }
docs: Adds an {@link OnTextSizeChangeListener} to the list of those whose methods are called
  whenever the {@link TextView}'s {@code textSize} changes.