Fix various warnings and errors in html_diff and its annotations.

utils/apidoc/html_diff.dart

 // Copyright (c) 2011, 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 67 matching lines @@
   final Map<Member, Set<Member>> htmlToDom;
 
   /** A map from `dart:dom` types to corresponding `dart:html` types. */
   final Map<Type, Set<Type>> domTypesToHtml;
 
   /** A map from `dart:html` types to corresponding `dart:dom` types. */
   final Map<Type, Set<Type>> htmlTypesToDom;
 
   final CommentMap comments;
 
-  final Library dom;
+  static Library dom;
 
   /**
    * Perform static initialization of [world]. This should be run before
    * calling [HtmlDiff.run].
    */
   static void initialize() {
     world.processDartScript('dart:htmlimpl');
     world.resolveAll();
     dom = world.libraries['dart:dom'];
   }
@@ skipping 329 matching lines @@
   Map<String, String> _getTags(String comment) {
     if (comment == null) return const <String>{};
     final re = new RegExp("@([a-zA-Z]+) ([^;]+)(?:;|\$)");
     final tags = <String>{};
     for (var m in re.allMatches(comment.trim())) {
       tags[m[1]] = m[2];
     }
     return tags;
   }
 }