code: function findNearestCommonParentChunk(chunkGroups, currentDistance = 0) {
    // Map of chunk name to distance from target
    const distances = new Map();
    for (let i = 1; i < chunkGroups.length; i++) {
      const distance = findAncestorDistance(
        chunkGroups[i],
        chunkGroups[0],
        currentDistance
      );
      if (distance < 0) {
        distances.delete(chunkGroups[0]);
      } else if (
        !distances.has(chunkGroups[0]) ||
        distance < distances.get(chunkGroups[0])
      ) {
        distances.set(chunkGroups[0], distance);
      }
    }
    if (distances.size === 0) {
      // chunkGroup[0] was not a parent for the other chunk groups.
      // So move up the graph one level and check again.
      chunkGroups[0].getParents().forEach((chunkGroupParent) => {
        const distanceRecord = findNearestCommonParentChunk(
          [chunkGroupParent].concat(chunkGroups.slice(1)),
          currentDistance + 1
        );
        if (
          distanceRecord.distance >= 0 &&
          (!distances.has(distanceRecord.chunkGroup) ||
            distances.get(distanceRecord.chunkGroup) < distanceRecord.distance)
        ) {
          distances.set(distanceRecord.chunkGroup, distanceRecord.distance);
        }
      });
    }
  
    const nearestCommonParent = {
      chunkGroup: undefined,
      distance: -1,
    };
    distances.forEach((distance, chunkGroup) => {
      if (
        nearestCommonParent.distance < 0 ||
        distance < nearestCommonParent.distance
      ) {
        nearestCommonParent.chunkGroup = chunkGroup;
        nearestCommonParent.distance = distance;
      }
    });
    return nearestCommonParent;
  }
docs: Find the closest common parent chunk from a list.
  Since closure-compiler requires a chunk tree to have a single root,
  there will always be a common parent.
  
  @param {!Array<string>} chunkGroups
  @param {number} currentDistance
  @return {{chunkGroup: (!ChunkGroup|undefined), distance: number}}