Upstream needs this to deal with size_t, but our low-level DES APIs take
size_t, so this is not a concern.
Change-Id: I9dc4c7248c5dd9515246a4b224147b932328a400
Reviewed-on: https://boringssl-review.googlesource.com/3882
Reviewed-by: Adam Langley <agl@google.com>