Allow Object when doing lookups.

sdk/lib/collection/iterable.dart

 // Copyright (c) 2012, 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;
 
 /**
  * This [Iterable] mixin implements all [Iterable] members except `iterator`.
  *
  * All other methods are implemented in terms of `iterator`.
  */
 abstract class IterableMixin<E> implements Iterable<E> {
   Iterable map(f(E element)) => new MappedIterable<E, dynamic>(this, f);
 
   Iterable<E> where(bool f(E element)) => new WhereIterable<E>(this, f);
 
   Iterable expand(Iterable f(E element)) =>
       new ExpandIterable<E, dynamic>(this, f);
 
-  bool contains(E element) {
+  bool contains(Object element) {
     for (E e in this) {
       if (e == element) return true;
     }
     return false;
   }
 
   void forEach(void f(E element)) {
     for (E element in this) f(element);
   }
 
@@ skipping 173 matching lines @@
   // to combine const constructors and mixins.
   const IterableBase();
 
   Iterable map(f(E element)) => new MappedIterable<E, dynamic>(this, f);
 
   Iterable<E> where(bool f(E element)) => new WhereIterable<E>(this, f);
 
   Iterable expand(Iterable f(E element)) =>
       new ExpandIterable<E, dynamic>(this, f);
 
-  bool contains(E element) {
+  bool contains(Object element) {
     for (E e in this) {
       if (e == element) return true;
     }
     return false;
   }
 
   void forEach(void f(E element)) {
     for (E element in this) f(element);
   }
 
@@ skipping 154 matching lines @@
   E elementAt(int index) {
     if (index is! int || index < 0) throw new RangeError.value(index);
     int remaining = index;
     for (E element in this) {
       if (remaining == 0) return element;
       remaining--;
     }
     throw new RangeError.value(index);
   }
 }