Eliminate dependencies on pkg/front_end.

pkg/analyzer/lib/src/generated/timestamped_data.dart

Index: pkg/analyzer/lib/src/generated/timestamped_data.dart
diff --git a/pkg/analyzer/lib/src/generated/timestamped_data.dart b/pkg/analyzer/lib/src/generated/timestamped_data.dart
new file mode 100644
index 0000000000000000000000000000000000000000..917fb1f97c32c8de8f2e9f99aef1c7bfcda47270
--- /dev/null
+++ b/pkg/analyzer/lib/src/generated/timestamped_data.dart
@@ -0,0 +1,8 @@
+// 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.
+
+// This library re-exports front_end's timestamped_data.dart, since its API is
+// stable enough to be relied upon by clients.
+
+export 'package:front_end/src/base/timestamped_data.dart' show TimestampedData;