Make summary format stable when adding getters to idl.

pkg/analyzer/tool/summary/idl_model.dart

 // Copyright (c) 2015, 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 file contains a set of concrete classes representing an in-memory
  * semantic model of the IDL used to code generate summary serialization and
  * deserialization code.
  */
 library analyzer.tool.summary.idl_model;
@@ skipping 56 matching lines @@
 
 /**
  * Information about a single class field defined in the IDL.
  */
 class FieldDeclaration extends Declaration {
   /**
    * The file of the field.
    */
   final FieldType type;
 
-  FieldDeclaration(String documentation, String name, this.type)
+  /**
+   * The id of the field.
+   */
+  final int id;
+
+  FieldDeclaration(String documentation, String name, this.type, this.id)
       : super(documentation, name);
 }
 
 /**
  * Information about the type of a class field defined in the IDL.
  */
 class FieldType {
   /**
    * Type of the field (e.g. 'int').
    */
@@ skipping 15 matching lines @@
   /**
    * Classes defined in the IDL.
    */
   final Map<String, ClassDeclaration> classes = <String, ClassDeclaration>{};
 
   /**
    * Enums defined in the IDL.
    */
   final Map<String, EnumDeclaration> enums = <String, EnumDeclaration>{};
 }