refactor(3p/nix): Apply clang-tidy's performance-* fixes r/789

This applies the performance fixes listed here:

https://clang.llvm.org/extra/clang-tidy/checks/list.html

1 files changed, 1 insertions, 1 deletions

diff --git a/third_party/nix/src/libstore/download.hh b/third_party/nix/src/libstore/download.hh
index 5e7bbf4ad6..9ddbdfc159 100644
--- a/third_party/nix/src/libstore/download.hh
+++ b/third_party/nix/src/libstore/download.hh
@@ -108,7 +108,7 @@ struct Downloader {
      and is more recent than ‘tarball-ttl’ seconds. Otherwise,
      use the recorded ETag to verify if the server has a more
      recent version, and if so, download it to the Nix store. */
-  CachedDownloadResult downloadCached(ref<Store> store,
+  CachedDownloadResult downloadCached(const ref<Store>& store,
                                       const CachedDownloadRequest& request);
 
   enum Error { NotFound, Forbidden, Misc, Transient, Interrupted };