Add a much simplified set implementation designed to waste little memory for small sets.

sdk/lib/_internal/compiler/implementation/util/util.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.
 
 library dart2js.util;
 
 import "dart:collection";
 import 'util_implementation.dart';
 import 'characters.dart';
 
+export 'setlet.dart';
+
 part 'link.dart';
 part 'expensive_map.dart';
 part 'expensive_set.dart';
 
 /**
  * Tagging interface for classes from which source spans can be generated.
  */
 // TODO(johnniwinther): Find a better name.
 // TODO(ahe): How about "Bolt"?
 abstract class Spannable {}
@@ skipping 260 matching lines @@
   }
   buffer.write(string);
 }
 
 int computeHashCode(part1, [part2, part3, part4]) {
   return (part1.hashCode
           ^ part2.hashCode
           ^ part3.hashCode
           ^ part4.hashCode) & 0x3fffffff;
 }