Sort strings in the index.

pkg/analyzer/lib/src/summary/idl.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 is an "idl" style description of the summary format.  It
  * contains abstract classes which declare the interface for reading data from
  * summaries.  It is parsed and transformed into code that implements the
  * summary format.
  *
@@ skipping 548 matching lines @@
 
   /**
    * Each item of this list corresponds to a unique referenced element.  It is
    * the index into [unitLibraryUris] and [unitUnitUris] for the library
    * specific unit where the element is declared.
    */
   @Id(0)
   List<int> get elementUnits;
 
   /**
-   * List of unique element strings used in this [PackageIndex].
+   * List of unique element strings used in this [PackageIndex].  The list is
+   * sorted in ascending order, so that the client can quickly check the
+   * presence of a string in this [PackageIndex].
    */
   @Id(6)
   List<String> get strings;
 
   /**
    * Each item of this list corresponds to the library URI of a unique library
    * specific unit referenced in the [PackageIndex].  It is an index into
    * [strings] list.
    */
   @Id(2)
@@ skipping 1760 matching lines @@
    */
   @Id(11)
   int get visibleLength;
 
   /**
    * If a local variable, the beginning of the visible range; zero otherwise.
    */
   @Id(12)
   int get visibleOffset;
 }