move comment tokens into preceedingComments 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;
 
   /**
+   * 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.
    *
    * Defined as getter to save a field in the [KeywordToken] subclass.
    */
   PrecedenceInfo get info;
 
   /**
    * The string represented by this token, a substring of the source code.
    *
@@ skipping 309 matching lines @@
       identical(value, "<=") ||
       identical(value, "<") ||
       identical(value, "&") ||
       identical(value, "^") ||
       identical(value, "|");
 }
 
 bool isTernaryOperator(String value) => identical(value, "[]=");
 
 bool isMinusOperator(String value) => identical(value, "-");