code: func (dc *inactiveChainReplicator) TrackChain(chain string, genesisBlock *common.Block, createChainCallback etcdraft.CreateChainCallback) {
  	if genesisBlock == nil {
  		dc.logger.Panicf("Called with a nil genesis block")
  	}
  	dc.lock.Lock()
  	defer dc.lock.Unlock()
  	dc.logger.Infof("Adding %s to the set of chains to track", chain)
  	dc.chains2CreationCallbacks[chain] = chainCreation{
  		genesisBlock: genesisBlock,
  		create:       createChainCallback,
  	}
  }
docs: // TrackChain tracks a chain with the given name, and calls the given callback
  // when this chain should be activated.