docs: private DrawableParent getParentDrawableAtIndex(int index) {
      DrawableParent parent = mFadeDrawable.getDrawableParentForIndex(index);
      if (parent.getDrawable() instanceof MatrixDrawable) {
        parent = (MatrixDrawable) parent.getDrawable();
      }
      if (parent.getDrawable() instanceof ScaleTypeDrawable) {
        parent = (ScaleTypeDrawable) parent.getDrawable();
      }
      return parent;
    }