message: Use ProtobufTypes::String for LocalityLess
  The string values are coming out of a protobuf, so use the protobuf
  string types.
diff: @@ -24,7 +24,8 @@ struct LocalityEqualTo {
  struct LocalityLess {
  bool operator()(const envoy::api::v2::core::Locality& lhs,
  const envoy::api::v2::core::Locality& rhs) const {
  - using LocalityTuple = std::tuple<const std::string&, const std::string&, const std::string&>;
  + using LocalityTuple = std::tuple<const ProtobufTypes::String&, const ProtobufTypes::String&,
  + const ProtobufTypes::String&>;
  const LocalityTuple lhs_tuple = LocalityTuple(lhs.region(), lhs.zone(), lhs.sub_zone());
  const LocalityTuple rhs_tuple = LocalityTuple(rhs.region(), rhs.zone(), rhs.sub_zone());
  return lhs_tuple < rhs_tuple;
  