docs: public void setOverlayImage(int index, @Nullable Drawable drawable) {
      // Note that overlays are by definition top-most and therefore the last elements in the array.
      Preconditions.checkArgument(
          index >= 0 && OVERLAY_IMAGES_INDEX + index < mFadeDrawable.getNumberOfLayers(),
          "The given index does not correspond to an overlay image.");
      setChildDrawableAtIndex(OVERLAY_IMAGES_INDEX + index, drawable);
    }