Add a suppression for a datarace in proto on an idempotent write
diff --git a/tools/tsan_suppressions.txt b/tools/tsan_suppressions.txt
index 09e68cd..765fa09 100644
--- a/tools/tsan_suppressions.txt
+++ b/tools/tsan_suppressions.txt
@@ -6,3 +6,6 @@
 race:ssleay_rand_add
 race:ssleay_rand_bytes
 race:__sleep_for
+# protobuf has an idempotent write race in ByteSize
+# https://github.com/google/protobuf/issues/2169
+race:ByteSize