message: Prototype for boundary functions
diff: @@ -302,12 +302,24 @@ class Roadgraph {
  std::pair<XodrLaneId, bool> GetNextLane(
  const std::vector<XodrRoadId>& road_ids,
  const XodrLaneId& lane_id);
  - // XodrLaneId GetNextLane(const XodrLaneId& lane_id) {}
  - XodrRoadId GetNextRoad(const XodrRoadId& road_id) {}
  +
  XodrLaneId GetLeftBoundary(const XodrLaneId& lane_id,
  - const XodrDrivingDirection& driving_direction) {}
  + const XodrDrivingDirection& driving_direction) {
  + // if (forwards and negative) -> inner
  + // if (forwards and positive) -> outer
  +
  + // if (backwards and positive) -> inner
  + // if (backwards and negative) -> outer
  + }
  +
  XodrLaneId GetRightBoundary(const XodrLaneId& lane_id,
  - const XodrDrivingDirection& driving_direction) {}
  + const XodrDrivingDirection& driving_direction) {
  + // if (forwards and negative) -> outer
  + // if (forwards and positive) -> inner
  +
  + // if (backwards and positive) -> outer
  + // if (backwards and negative) -> inner
  + }
  modules::geometry::Line GetCenterLine(const XodrLaneId& lane_id) {}
  