code: function findActivePipeline(pipelineId, isRoot) {
    var infoMap = STATUS_MAP.pipelines[pipelineId];
    if (!infoMap) {
      return null;
    }
  
    // This is an active leaf node.
    if (infoMap.children.length == 0 && infoMap.status != 'done') {
      return pipelineId;
    }
  
    // Sort children by start time only.
    var children = infoMap.children.slice(0);
    children.sort(function(a, b) {
      var infoMapA = STATUS_MAP.pipelines[a];
      var infoMapB = STATUS_MAP.pipelines[b];
      if (!infoMapA || !infoMapB) {
        return 0;
      }
      if (infoMapA.startTimeMs && infoMapB.startTimeMs) {
        return infoMapA.startTimeMs - infoMapB.startTimeMs;
      } else {
        return 0;
      }
    });
  
    for (var i = 0; i < children.length; ++i) {
      var foundPipelineId = findActivePipeline(children[i], false);
      if (foundPipelineId != null) {
        return foundPipelineId;
      }
    }
  
    return null;
  }
docs: Depth-first search for active pipeline.