message: tperf: fix per-stream stats summary
diff: @@ -340,9 +340,9 @@ class TPerfClient : public quic::QuicSocket::ConnectionCallback,
  }
  std::ostringstream os;
  bytesPerStreamHistogram_.toTSV(os);
  - std::vector<folly::StringPiece> lines;
  + std::vector<std::string> lines;
  folly::split("\n", os.str(), lines);
  - for (const auto line : lines) {
  + for (const auto& line : lines) {
  LOG(INFO) << line;
  }
  }
  