message: Fix open source build. Depending on the typedefs, this needs to be size_t.
diff: @@ -36,7 +36,7 @@ class HkdfInputStream : public InputStream {
  stream_status_ = util::OkStatus();
  ResizeStringUninitialized(&prk_, EVP_MAX_MD_SIZE);
  - uint64_t prk_len;
  + size_t prk_len;
  if (1 != HKDF_extract(
  reinterpret_cast<uint8_t *>(&prk_[0]), &prk_len, digest_,
  