Allow Object when doing lookups.

sdk/lib/_collection_dev/iterable.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.
 
 part of dart._collection.dev;
 
 /**
  * An [Iterable] for classes that have efficient [length] and [elementAt].
  *
  * All other methods are implemented in terms of [length] and [elementAt],
@@ skipping 28 matching lines @@
     if (length == 0) throw new StateError("No elements");
     return elementAt(length - 1);
   }
 
   E get single {
     if (length == 0) throw new StateError("No elements");
     if (length > 1) throw new StateError("Too many elements");
     return elementAt(0);
   }
 
-  bool contains(E element) {
+  bool contains(Object element) {
     int length = this.length;
     for (int i = 0; i < length; i++) {
       if (elementAt(i) == element) return true;
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     return false;
   }
 
@@ skipping 540 matching lines @@
   int get length => 0;
 
   E get first { throw new StateError("No elements"); }
 
   E get last { throw new StateError("No elements"); }
 
   E get single { throw new StateError("No elements"); }
 
   E elementAt(int index) { throw new RangeError.value(index); }
 
-  bool contains(E element) => false;
+  bool contains(Object element) => false;
 
   bool every(bool test(E element)) => true;
 
   bool any(bool test(E element)) => false;
 
   E firstWhere(bool test(E element), { E orElse() }) {
     if (orElse != null) return orElse();
     throw new StateError("No matching element");
   }
 
@@ skipping 414 matching lines @@
 
   static Set setDifference(Set set, Set other, Set result) {
     for (var element in set) {
       if (!other.contains(element)) {
         result.add(element);
       }
     }
     return result;
   }
 }