Require two type arguments for map literals (issue 4522).

utils/apidoc/html_diff.dart

 // Copyright (c) 2012, 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.
 
 /**
  * A script to assist in documenting the difference between the dart:html API
  * and the old DOM API.
  */
 #library('html_diff');
 
@@ skipping 261 matching lines @@
 
   /**
    * Extracts a [Map] from tag names to values from [comment], which is parsed
    * from a Dart source file via dartdoc. Tags are of the form `@NAME VALUE`,
    * where `NAME` is alphabetic and `VALUE` can contain any character other than
    * `;`. Multiple tags can be separated by semicolons.
    *
    * At time of writing, the only tag that's used is `@domName`.
    */
   Map<String, String> _getTags(String comment) {
-    if (comment == null) return const <String>{};
+    if (comment == null) return const <String, String>{};
     final re = const RegExp("@([a-zA-Z]+) ([^;]+)(?:;|\$)");
-    final tags = <String>{};
+    final tags = <String, String>{};
     for (var m in re.allMatches(comment.trim())) {
       tags[m[1]] = m[2];
     }
     return tags;
   }
 }