Use packages dart_parser, dart_scanner, and compiler_util.

pkg/compiler/lib/src/tree/unparser.dart

Index: pkg/compiler/lib/src/tree/unparser.dart
diff --git a/pkg/compiler/lib/src/tree/unparser.dart b/pkg/compiler/lib/src/tree/unparser.dart
index 5d1d15431e2515513ebce1d29aafb3477b20b002..cd13be321c6a506b6462a48ef99e9a87aee9a359 100644
--- a/pkg/compiler/lib/src/tree/unparser.dart
+++ b/pkg/compiler/lib/src/tree/unparser.dart
@@ -2,8 +2,8 @@
 // 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 '../tokens/token.dart' show Token;
-import '../tokens/token_constants.dart' as Tokens
+import 'package:dart_scanner/dart_scanner.dart' show Token;
+import 'package:dart_scanner/src/token_constants.dart' as Tokens
     show IDENTIFIER_TOKEN, KEYWORD_TOKEN, PLUS_TOKEN;
 import '../util/util.dart';
 import 'nodes.dart';