message: Public accessor for buffer size of flexbuffers::Builder
diff: @@ -802,6 +802,11 @@ class Builder FLATBUFFERS_FINAL_CLASS {
  return buf_;
  }
  + // Size of the buffer. Does not include unfinished values.
  + size_t GetSize() const {
  + return buf_.size();
  + }
  +
  // Reset all state so we can re-use the buffer.
  void Clear() {
  buf_.clear();
  