When copying TokenWithComment, use copy of its comments.

pkg/analyzer/lib/src/dart/ast/token.dart

 // Copyright (c) 2014, 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 analyzer.src.dart.ast.token;
 
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 
 /**
@@ skipping 551 matching lines @@
 
   @override
   CommentToken get precedingComments => _precedingComment;
 
   void set precedingComments(CommentToken comment) {
     _precedingComment = comment;
     _setCommentParent(_precedingComment);
   }
 
   @override
-  Token copy() => new TokenWithComment(type, offset, precedingComments);
+  Token copy() =>
+      new TokenWithComment(type, offset, copyComments(precedingComments));
 }