use proper notation for true, false, and null in doc comments

sdk/lib/_internal/compiler/implementation/dump_info.dart

 // Copyright (c) 2013, 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 dump_info;
 
 import 'elements/elements.dart';
 import 'elements/visitor.dart';
 import 'dart:convert' show HtmlEscape;
 import 'dart2jslib.dart' show
@@ skipping 59 matching lines @@
 /// An [ElementNode] holds information about an [Element]
 class ElementInfoNode implements InfoNode {
   /// The name of the represented [Element].
   final String name;
 
   /// The kind of the [Element] represented.  This is presented to the
   /// user, so it might be more specific than [element.kind].
   final String kind;
 
   /// The static type of the represented [Element].
-  /// [null] if this kind of element has no type.
+  /// [:null:] if this kind of element has no type.
   final String type;
 
   /// Any extra information to display about the represented [Element].
   final String extra;
 
   /// A textual description of the modifiers (such as "static", "abstract") of
   /// the represented [Element].
   final String modifiers;
 
   /// Describes how many bytes the code for the represented [Element] takes up
@@ skipping 401 matching lines @@
         var container = containers[i];
         container.addEventListener('click',
           toggler(container.nextElementSibling), false);
        container.nextElementSibling.hidden = true;
       };
     </script>
   </body>
 </html>""");
   }
 }