add previous token field

pkg/front_end/tool/fasta/compile.dart

Index: pkg/front_end/tool/fasta/compile.dart
diff --git a/pkg/front_end/tool/fasta/compile.dart b/pkg/front_end/tool/fasta/compile.dart
index 5deaaaddb22f1e64122ae989d3e20903fa6260ac..a087b7a7525c068e479e39e58f2ce43c3e023ac5 100644
--- a/pkg/front_end/tool/fasta/compile.dart
+++ b/pkg/front_end/tool/fasta/compile.dart
@@ -2,8 +2,6 @@
 // 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:math';
-
 import 'package:front_end/src/fasta/outline.dart' as outline;
 
 import 'standard_deviation.dart';