fix token type of first token in converted token stream

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 'package:front_end/src/fasta/parser/error_kind.dart' show
     ErrorKind;
 
 import 'package:front_end/src/fasta/scanner/error_token.dart' show
@@ skipping 74 matching lines @@
   ///
   /// The first element of this list is always a sentinel `null` value so that
   /// we don't have to check if it is empty.
   ///
   /// See additional documentation in [_matchGroups].
   List<Token> _endTokenStack;
 
   /// Converts a stream of Fasta tokens (starting with [token] and continuing to
   /// EOF) to a stream of analyzer tokens.
   analyzer.Token convertTokens(Token token) {
-    _analyzerTokenHead = new analyzer.Token(null, 0);
+    _analyzerTokenHead = new analyzer.Token(TokenType.EOF, -1);
     _analyzerTokenHead.previous = _analyzerTokenHead;
     _analyzerTokenTail = _analyzerTokenHead;
     _currentCommentHead = null;
     _currentCommentTail = null;
     _beginTokenStack = [null];
     _endTokenStack = <Token>[null];
 
     while (true) {
       if (token.info.kind == BAD_INPUT_TOKEN) {
         ErrorToken errorToken = token;
@@ skipping 602 matching lines @@
     case BACKSLASH_TOKEN: return TokenType.BACKSLASH;
     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}");
   }
 }