add previous token field

pkg/front_end/lib/src/fasta/scanner/token.dart

 // Copyright (c) 2011, 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.
 
 library fasta.scanner.token;
 
 import 'keyword.dart' show Keyword;
 
 import 'precedence.dart' show BAD_INPUT_INFO, EOF_INFO, PrecedenceInfo;
 
@@ skipping 11 matching lines @@
   final int charOffset;
 
   Token(this.charOffset);
 
   /**
    * The next token in the token stream.
    */
   Token next;
 
   /**
+   * The previous token in the token stream.
+   * @deprecated This exists for compatibility with the Analyzer token stream

[Paul Berry, 2017/03/07 13:47:28]

Saying "@deprecated" here doesn't have any effect on analysis.  If we want to
deprecate it, we should do:

@deprecated
Token previous;

so that references to it will be flagged by analyzer.

(Note that we can always suppress such warnings using the "// ignore:" syntax)

[danrubel, 2017/03/07 14:40:54]

Good catch. That's what I meant to do. Fixed.

+   * and will be removed at some future date.
+   */
+  Token previous;
+
+  /**
    * Return the first comment in the list of comments that precede this token,
    * or `null` if there are no comments preceding this token. Additional
    * comments can be reached by following the token stream using [next] until
    * `null` is returned.
    */
   Token precedingComments;
 
   /**
    * The precedence info for this token. [info] determines the kind and the
    * precedence level of this token.
@@ skipping 317 matching lines @@
       identical(value, "<=") ||
       identical(value, "<") ||
       identical(value, "&") ||
       identical(value, "^") ||
       identical(value, "|");
 }
 
 bool isTernaryOperator(String value) => identical(value, "[]=");
 
 bool isMinusOperator(String value) => identical(value, "-");