Compute topologically sorted library cycles.

pkg/front_end/lib/src/incremental_kernel_generator_impl.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 
 import 'package:front_end/file_system.dart';
 import 'package:front_end/incremental_kernel_generator.dart';
 import 'package:front_end/incremental_resolved_ast_generator.dart';
 import 'package:front_end/src/base/processed_options.dart';
@@ skipping 107 matching lines @@
 
   /// Refresh all the invalidated files and update dependencies.
   Future<Null> _refreshInvalidatedFiles() async {
     for (Uri fileUri in _invalidatedFiles) {
       FileState file = await _fsState.getFile(fileUri);
       await file.refresh();
     }
     _invalidatedFiles.clear();
   }
 }
-
-///// Clears canonical names of [NamedNode] references.
-//class _ClearCanonicalNamesVisitor extends Visitor {
-//  defaultNode(Node node) {
-//    if (node is NamedNode) {
-//      node.reference.canonicalName = null;
-//    }
-//    node.visitChildren(this);
-//  }
-//}