Fix bug in equalsIgnoreAsciiCase.

lib/src/equality.dart

 // Copyright (c) 2013, 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 "dart:collection";
 
+import "comparators.dart";
+
 const int _HASH_MASK = 0x7fffffff;
 
 /// A generic equality relation on objects.
 abstract class Equality<E> {
   const factory Equality() = DefaultEquality<E>;
 
   /// Compare two elements for being equal.
   ///
   /// This should be a proper equality relation.
   bool equals(E e1, E e2);
@@ skipping 372 matching lines @@
 class CaseInsensitiveEquality implements Equality<String> {
   const CaseInsensitiveEquality();
 
   bool equals(String string1, String string2) =>
       equalsIgnoreAsciiCase(string1, string2);
 
   int hash(String string) => hashIgnoreAsciiCase(string);
 
   bool isValidKey(Object object) => object is String;
 }