reuse memory in stream_sequencer_buffer

[ktprime]

in quic_stream_sequencer_buffer.cc

I make some change in my person project, during test most time only one memory block is used.(reduce new/free)

  void QuicStreamSequencerBuffer::Clear() {
  if (blocks_ != nullptr) {
    for (size_t i = 0; i < current_blocks_count_; ++i) {
      if (blocks_[i] != nullptr) {
        //RetireBlock(i);
        delete blocks_[index];
        blocks_[index] = nullptr;
      }
    }
  }
  num_bytes_buffered_ = 0;
  bytes_received_.Clear();
  bytes_received_.Add(0, total_bytes_read_);
}

//  DCHECK(max_buffer_capacity_bytes_ % kBlockSizeBytes  == 0);
bool QuicStreamSequencerBuffer::RetireBlock(size_t index) {
  if (blocks_[index] == nullptr) {
    QUIC_BUG(quic_bug_10610_1) << "Try to retire block twice";
    return false;
  }
  
  //keeping current block to use
  const auto block_finished = total_bytes_read_ % kBlockSizeBytes == 0;
  if (!block_finished)
   return true;

  //move current block to next
  const auto maybe_read_block = GetBlockIndex(total_bytes_read_ + num_bytes_buffered_ + kBlockSizeBytes);
  if (blocks_[maybe_read_block] == nullptr) {
    blocks_[maybe_read_block] = blocks_[index];
    blocks_[index] = nullptr;
  } else {  
    delete blocks_[index];
    blocks_[index] = nullptr;
  }
  QUIC_DVLOG(1) << "Retired block with index: " << index;
  return true;
}

[ktprime]

used in my project