constructor(indexBytes) {
    e2e.assert(
        indexBytes.length == INDEX_SIZE_BYTES_,
        'index is wrong size (' + indexBytes.length + ' bytes)',
        InvalidArgumentsError);
    /** @private @const */ this.indexBytes_ = indexBytes;
  }
@param {!e2e.ByteArray} indexBytes Index into the tree as a byte array.
@throws {!InvalidArgumentsError} If indexBytes is not exactly 32 bytes
    long.