Use packages dart_parser, dart_scanner, and compiler_util.

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

Index: pkg/compiler/lib/src/tree/prettyprint.dart
diff --git a/pkg/compiler/lib/src/tree/prettyprint.dart b/pkg/compiler/lib/src/tree/prettyprint.dart
index 837db3750ab7740eaa6c1967c8d54201c283105e..39c8ecc4bc450265833ae051ebb3cf4f2d44eea0 100644
--- a/pkg/compiler/lib/src/tree/prettyprint.dart
+++ b/pkg/compiler/lib/src/tree/prettyprint.dart
@@ -2,7 +2,7 @@
 // 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 'package:dart_scanner/dart_scanner.dart' show Token;
 import '../util/util.dart';
 import 'nodes.dart';