static filterVariantsByVideoLayout_(variants, videoLayout) {
    return variants.filter((variant) => {
      if (variant.video && variant.video.videoLayout &&
          variant.video.videoLayout != videoLayout) {
        return false;
      }
      return true;
    });
  }
Filters variants according to the given video layout config.

@param {!Array<shaka.extern.Variant>} variants
@param {string} videoLayout
@private