Add missing copyrights

pkg/front_end/test/src/dependency_walker_test.dart

Index: pkg/front_end/test/src/dependency_walker_test.dart
diff --git a/pkg/front_end/test/src/dependency_walker_test.dart b/pkg/front_end/test/src/dependency_walker_test.dart
index 74ed3b26a6835ec7400089709fd859bcdde71f97..d4c731bdbfed5d0ea6997a467467963b91578137 100644
--- a/pkg/front_end/test/src/dependency_walker_test.dart
+++ b/pkg/front_end/test/src/dependency_walker_test.dart
@@ -1,3 +1,7 @@
+// Copyright (c) 2016, 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 'package:front_end/src/dependency_walker.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';