Add the ability to convert an analyzer token stream to a Fasta one.

pkg/front_end/test/scanner_test.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.
 
 import 'package:front_end/src/base/errors.dart';
 import 'package:front_end/src/base/jenkins_smi_hash.dart';
 import 'package:front_end/src/scanner/errors.dart';
 import 'package:front_end/src/scanner/reader.dart';
 import 'package:front_end/src/scanner/scanner.dart';
 import 'package:front_end/src/scanner/token.dart';
@@ skipping 348 matching lines @@
   }
 
   void test_eq() {
     _assertToken(TokenType.EQ, "=");
   }
 
   void test_eq_eq() {
     _assertToken(TokenType.EQ_EQ, "==");
   }
 
+  void test_function() {
+    _assertToken(TokenType.FUNCTION, "=>");
+  }
+
   void test_gt() {
     _assertToken(TokenType.GT, ">");
   }
 
   void test_gt_eq() {
     _assertToken(TokenType.GT_EQ, ">=");
   }
 
   void test_gt_gt() {
     _assertToken(TokenType.GT_GT, ">>");
@@ skipping 1028 matching lines @@
   _TestScanner(CharacterReader reader, [this.listener]) : super(reader);
 
   @override
   void reportError(
       ScannerErrorCode errorCode, int offset, List<Object> arguments) {
     if (listener != null) {
       listener.errors.add(new TestError(offset, errorCode, arguments));
     }
   }
 }