Remember direct dependencies in LibraryCycle.

pkg/front_end/test/src/incremental/file_state_test.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/memory_file_system.dart';
 import 'package:front_end/src/fasta/uri_translator_impl.dart';
 import 'package:front_end/src/byte_store/byte_store.dart';
 import 'package:front_end/src/incremental/file_state.dart';
@@ skipping 398 matching lines @@
     FileState d = await fsState.getFile(dUri);
 
     List<LibraryCycle> cycles = d.topologicalOrder;
     expect(cycles, hasLength(4));
 
     expect(cycles[0].libraries, contains(core));
     expect(cycles[1].libraries, unorderedEquals([a]));
     expect(cycles[2].libraries, unorderedEquals([b, c]));
     expect(cycles[3].libraries, unorderedEquals([d]));
 
+    expect(cycles[0].directDependencies, isEmpty);
+    expect(cycles[1].directDependencies, unorderedEquals([cycles[0]]));
+    expect(cycles[2].directDependencies, unorderedEquals([cycles[0]]));
+    expect(cycles[3].directDependencies,
+        unorderedEquals([cycles[0], cycles[1], cycles[2]]));
+
     expect(cycles[0].directUsers,
         unorderedEquals([cycles[1], cycles[2], cycles[3]]));
     expect(cycles[1].directUsers, unorderedEquals([cycles[3]]));
     expect(cycles[2].directUsers, unorderedEquals([cycles[3]]));
     expect(cycles[3].directUsers, isEmpty);
   }
 
   test_topologicalOrder_cycleBeforeTarget_export() async {
     var aUri = _writeFileDirectives('/a.dart');
     var bUri = _writeFileDirectives('/b.dart', exports: ['c.dart']);
@@ skipping 81 matching lines @@
   }
 
   Uri _writeFileDirectives(String path,
       {List<String> imports: const [], List<String> exports: const []}) {
     return writeFile(path, '''
 ${imports.map((uri) => 'import "$uri";').join('\n')}
 ${exports.map((uri) => 'export "$uri";').join('\n')}
 ''');
   }
 }