Add magenta/benchmarks to list-of-repos in gitsync.

Change-Id: If49f99a6530a47fdd649f89800e3f2c2a632c118
diff --git a/scripts/gitsync/list-of-repos.txt b/scripts/gitsync/list-of-repos.txt
index c9757a1..314300e 100644
--- a/scripts/gitsync/list-of-repos.txt
+++ b/scripts/gitsync/list-of-repos.txt
@@ -27,6 +27,7 @@
 llvm-passes
 logging
 magenta
+magenta/benchmarks
 magma
 manifest
 maxwell