fix for return type issue in 22524

pkg/serialization/lib/serialization.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.
 
 /**
  * This provides a general-purpose serialization facility for Dart objects. A
  * [Serialization] is defined in terms of [SerializationRule]s and supports
  * reading and writing to different formats.
  *
  * ## Installing ##
@@ skipping 249 matching lines @@
     if (_selfDescribing != null) return _selfDescribing;
     return !rules.any((x) => x is CustomRule);
   }
 
   /**
    * When we write out data using this serialization, should we also write
    * out a description of the rules. This is on by default unless using
    * CustomRule subclasses, in which case it requires additional setup and
    * is off by default.
    */
-  void set selfDescribing(bool value) => _selfDescribing = value;
+  void set selfDescribing(bool value) {
+    _selfDescribing = value;
+  }
 
   /**
    * Creates a new serialization with a default set of rules for primitives
    * and lists.
    */
   Serialization() {
     addDefaultRules();
   }
 
   /**
@@ skipping 205 matching lines @@
 }
 
 /**
  * An exception class for errors during serialization.
  */
 class SerializationException implements Exception {
   final String message;
   const SerializationException([this.message]);
   toString() => "SerializationException($message)";
 }