message: Use pointer instead of reference for non-const argument
diff: @@ -372,7 +372,7 @@ static void CopyTreeStructure(
  class ColumnSchemaAggregator {
  public:
  void Collect(const ColumnPositionTree& columns) {
  - CollectColumnsTree(columns, columns_);
  + CollectColumnsTree(columns, &columns_);
  }
  // Sort columns by syntax tree path assigned to them and create an index that
  @@ -413,26 +413,27 @@ class ColumnSchemaAggregator {
  private:
  void CollectColumnsTree(const ColumnPositionTree& column,
  - VectorTree<AggregateColumnData>& aggregate_column) {
  + VectorTree<AggregateColumnData>* aggregate_column) {
  + CHECK_NOTNULL(aggregate_column);
  for (const auto& subcolumn : column.Children()) {
  const auto [index_entry, insert] =
  syntax_to_columns_map_.try_emplace(subcolumn.Value().path);
  VectorTree<verible::AggregateColumnData>* aggregate_subcolumn;
  if (insert) {
  - aggregate_subcolumn = aggregate_column.NewChild();
  + aggregate_subcolumn = aggregate_column->NewChild();
  CHECK_NOTNULL(aggregate_subcolumn);
  // Put aggregate column node's path in created index entry
  aggregate_subcolumn->Path(index_entry->second);
  } else {
  // Fact: existing aggregate_subcolumn is a direct child of
  // aggregate_column
  - CHECK_GT(aggregate_column.Children().size(),
  + CHECK_GT(aggregate_column->Children().size(),
  index_entry->second.back());
  aggregate_subcolumn =
  - &aggregate_column.Children()[index_entry->second.back()];
  + &aggregate_column->Children()[index_entry->second.back()];
  }
  aggregate_subcolumn->Value().Import(subcolumn.Value());
  - CollectColumnsTree(subcolumn, *aggregate_subcolumn);
  + CollectColumnsTree(subcolumn, aggregate_subcolumn);
  }
  }
  