Combine unmodifiable_collection package into collection_helpers.

pkg/collection_helpers/lib/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.
 
 /**
  * Defines equality relations on collections.
  */
-library dart.collection_helper.equality;
+library dart.collection_helpers.equality;
 
 import "dart:collection";
 
 const int _HASH_MASK = 0x7fffffff;
 
 /**
  * A generic equality relation on objects.
  */
 abstract class Equality<E> {
   const factory Equality() = DefaultEquality;
@@ skipping 391 matching lines @@
       if (o is List) return new ListEquality(this).hash(o);
       if (o is Iterable) return new IterableEquality(this).hash(o);
     } else if (o is Iterable) {
       return new UnorderedIterableEquality(this).hash(o);
     }
     return _base.hash(o);
   }
 
   bool isValidKey(Object o) => o is Iterable || o is Map || _base.isValidKey(o);
 }