code: protected ManagedChannel createManagedPool(String host, int channelCount) throws IOException {
      ManagedChannel channelPool = createChannelPool(host, channelCount);
      managedChannels.add(channelPool);
      return channelPool;
    }
docs: Create a new {@link com.google.cloud.bigtable.grpc.io.ChannelPool}, with auth headers, that
  will be cleaned up when the connection closes.
  
  @param host a {@link java.lang.String} object.
  @return a {@link com.google.cloud.bigtable.grpc.io.ChannelPool} object.
  @throws java.io.IOException if any.