add previous token field

pkg/front_end/lib/src/fasta/analyzer/token_utils.dart

 // Copyright (c) 2016, 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.analyzer.token_utils;
 
 import '../parser/error_kind.dart' show ErrorKind;
 
 import '../scanner/error_token.dart' show ErrorToken;
 
@@ skipping 264 matching lines @@
 
   Token translateComments(analyzer.Token token) {
     if (token == null) {
       return null;
     }
     Token head = fromAnalyzerToken(token);
     Token tail = head;
     token = token.next;
     while (token != null) {
       tail.next = fromAnalyzerToken(token);
+      tail.next.previousToken = tail;
       tail = tail.next;
       token = token.next;
     }
     return head;
   }
 
   analyzer.Token translateAndAppend(analyzer.Token analyzerToken) {
     var token = fromAnalyzerToken(analyzerToken);
     token.precedingComments =
         translateComments(analyzerToken.precedingComments);
     tokenTail.next = token;
+    tokenTail.next.previousToken = tokenTail;
     tokenTail = token;
     matchGroups(analyzerToken, token);
     return analyzerToken.next;
   }
 
   while (true) {
     // TODO(paulberry): join up begingroup/endgroup.
     if (analyzerToken.type == TokenType.EOF) {
       tokenTail.next = new SymbolToken(EOF_INFO, analyzerToken.offset);
+      tokenTail.next.previousToken = tokenTail;
       tokenTail.next.precedingComments =
           translateComments(analyzerToken.precedingComments);
       return tokenHead.next;
     }
     analyzerToken = translateAndAppend(analyzerToken);
   }
 }
 
 /// Converts a single analyzer token into a Fasta token.
 Token fromAnalyzerToken(analyzer.Token token) {
@@ skipping 460 matching lines @@
     case PERIOD_PERIOD_PERIOD_TOKEN:
       return TokenType.PERIOD_PERIOD_PERIOD;
     // case GENERIC_METHOD_TYPE_LIST_TOKEN:
     //   return TokenType.GENERIC_METHOD_TYPE_LIST;
     // case GENERIC_METHOD_TYPE_ASSIGN_TOKEN:
     //   return TokenType.GENERIC_METHOD_TYPE_ASSIGN;
     default:
       return internalError("Unhandled token ${token.info}");
   }
 }