docs: public DrawableParent getDrawableParentForIndex(int index) {
      Preconditions.checkArgument(index >= 0);
      Preconditions.checkArgument(index < mDrawableParents.length);
      if (mDrawableParents[index] == null) {
        mDrawableParents[index] = createDrawableParentForIndex(index);
      }
      return mDrawableParents[index];
    }