improve fasta export directive recovery

pkg/compiler/lib/src/parser/element_listener.dart

 // Copyright (c) 2015, 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 dart2js.parser.element_listener;
 
 import 'package:front_end/src/fasta/fasta_codes.dart' show Message;
 
 import 'package:front_end/src/fasta/fasta_codes.dart' as codes;
 
@@ skipping 526 matching lines @@
     pushNode(null);
   }
 
   Token handleError(Token token, Message message) {
     MessageKind errorCode;
     Map<String, dynamic> arguments = message.arguments;
 
     switch (message.code.dart2jsCode) {
       case "MISSING_TOKEN_BEFORE_THIS":
         String expected = arguments["string"];
+        // TODO(danrubel) This functionality is being replaced by

[ahe, 2017/08/22 12:27:00]

Add colon after "(danrubel)".

[danrubel, 2017/08/25 15:30:18]

Fixed in https://codereview.chromium.org/3003263002/

+        // the parser's ensureSemicolon method.
         if (identical(";", expected)) {
           // When a semicolon is missing, it often leads to an error on the
           // following line. So we try to find the token preceding the semicolon
           // and report that something is missing *after* it.
           Token preceding = findPrecedingToken(token);
           if (preceding == token) {
             reportErrorFromToken(token, MessageKind.MISSING_TOKEN_BEFORE_THIS,
                 {'token': expected});
           } else {
             reportErrorFromToken(preceding,
@@ skipping 386 matching lines @@
       memberErrors = memberErrors.tail.prepend(true);
     }
     reporter.reportErrorMessage(spannable, errorCode, arguments);
   }
 
   void reportErrorFromToken(Token token, MessageKind errorCode,
       [Map arguments = const {}]) {
     reportError(reporter.spanFromToken(token), errorCode, arguments);
   }
 }