improve fasta parser export declaration recovery

pkg/front_end/lib/src/fasta/fasta_codes_generated.dart

 // Copyright (c) 2017, 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.
 
 // NOTE: THIS FILE IS GENERATED. DO NOT EDIT.
 //
 // Instead modify 'pkg/front_end/messages.yaml' and run
 // 'pkg/front_end/tool/_fasta/generate_messages.dart' to update.
 
 part of fasta.codes;
@@ skipping 495 matching lines @@
   return new FastaMessage(uri, charOffset, codeUnsupportedPrefixPlus,
       message: "'+' is not a prefix operator. ",
       tip: "Try removing '+'.",
       arguments: {});
 }
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const FastaCode<_ExpectedString> codeExpectedString =
     const FastaCode<_ExpectedString>("ExpectedString",
         template: r"Expected a String, but got '#lexeme'.",
+        analyzerCode: "EXPECTED_STRING_LITERAL",
         dart2jsCode: "FASTA_FATAL",
         format: _formatExpectedString);
 
 typedef FastaMessage _ExpectedString(Uri uri, int charOffset, Token token);
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 FastaMessage _formatExpectedString(Uri uri, int charOffset, Token token) {
   String lexeme = token.lexeme;
   return new FastaMessage(uri, charOffset, codeExpectedString,
       message: "Expected a String, but got '$lexeme'.",
@@ skipping 595 matching lines @@
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 FastaMessage _formatNonAsciiIdentifier(
     Uri uri, int charOffset, String character, int codePoint) {
   String unicode = "(U+${codePoint.toRadixString(16).padLeft(4, '0')})";
   return new FastaMessage(uri, charOffset, codeNonAsciiIdentifier,
       message:
           "The non-ASCII character '$character' ($unicode) can't be used in identifiers, only in strings and comments.",
       tip: "Try using an US-ASCII letter, a digit, '_' (an underscore), or '\$' (a dollar sign).",
       arguments: {'character': character, 'codePoint': codePoint});
 }