Define equality for boolean selectors.

lib/src/impl.dart

 // Copyright (c) 2016, 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.
 
 import '../boolean_selector.dart';
 import 'ast.dart';
 import 'evaluator.dart';
 import 'intersection_selector.dart';
 import 'parser.dart';
 import 'union_selector.dart';
@@ skipping 35 matching lines @@
     return other is BooleanSelectorImpl
         ? new BooleanSelectorImpl._(new OrNode(_selector, other._selector))
         : new UnionSelector(this, other);
   }
 
   void validate(bool isDefined(String variable)) {
     _selector.accept(new Validator(isDefined));
   }
 
   String toString() => _selector.toString();
+
+  bool operator==(other) =>
+      other is BooleanSelectorImpl && _selector == other._selector;
+
+  int get hashCode => _selector.hashCode;
 }