message: tperf: histogram of bytes per stream
  Summary: per stream stats.
diff: #include <folly/init/Init.h>
  #include <folly/io/async/HHWheelTimer.h>
  #include <folly/portability/GFlags.h>
  +#include <folly/stats/Histogram.h>
  #include <quic/client/QuicClientTransport.h>
  #include <quic/common/test/TestUtils.h>
  @@ -326,10 +327,25 @@ class TPerfClient : public quic::QuicSocket::ConnectionCallback,
  LOG(INFO) << "Overall throughput: "
  << (receivedBytes_ / bytesPerMegabit) / duration_.count()
  << "Mb/s";
  - LOG(INFO) << "Per Stream throughput: "
  + // Per Stream Stats
  + LOG(INFO) << "Average per Stream throughput: "
  << ((receivedBytes_ / receivedStreams_) / bytesPerMegabit) /
  duration_.count()
  << "Mb/s over " << receivedStreams_ << " streams";
  + if (receivedStreams_ != 1) {
  + LOG(INFO) << "Histogram per Stream bytes: " << std::endl;
  + LOG(INFO) << "Lo\tHi\tNum\tSum";
  + for (const auto bytes : bytesPerStream_) {
  + bytesPerStreamHistogram_.addValue(bytes.second);
  + }
  + std::ostringstream os;
  + bytesPerStreamHistogram_.toTSV(os);
  + std::vector<folly::StringPiece> lines;
  + folly::split("\n", os.str(), lines);
  + for (const auto line : lines) {
  + LOG(INFO) << line;
  + }
  + }
  }
  virtual void callbackCanceled() noexcept override {}
  @@ -343,6 +359,11 @@ class TPerfClient : public quic::QuicSocket::ConnectionCallback,
  auto readBytes = readData->first->computeChainDataLength();
  receivedBytes_ += readBytes;
  + bytesPerStream_[streamId] += readBytes;
  + if (readData.value().second) {
  + bytesPerStreamHistogram_.addValue(bytesPerStream_[streamId]);
  + bytesPerStream_.erase(streamId);
  + }
  }
  void readError(
  @@ -452,6 +473,10 @@ class TPerfClient : public quic::QuicSocket::ConnectionCallback,
  folly::EventBase eventBase_;
  uint64_t receivedBytes_{0};
  uint64_t receivedStreams_{0};
  + std::map<quic::StreamId, uint64_t> bytesPerStream_;
  + folly::Histogram<uint64_t> bytesPerStreamHistogram_{1024,
  + 0,
  + 1024 * 1024 * 1024};
  std::chrono::seconds duration_;
  uint64_t window_;
  bool gso_;
  