Allow Object when doing lookups.

sdk/lib/core/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.core;
 
 /**
  * The [Iterable] interface allows to get an [Iterator] out of an
  * [Iterable] object.
  *
@@ skipping 58 matching lines @@
    * by [f] for each element of this, in order.
    *
    * The returned [Iterable] is lazy, and will call [f] for each element
    * of this every time it's iterated.
    */
   Iterable expand(Iterable f(E element));
 
   /**
    * Check whether the collection contains an element equal to [element].
    */
-  bool contains(E element);
+  bool contains(Object element);
 
   /**
    * Applies the function [f] to each element of this collection.
    */
   void forEach(void f(E element));
 
   /**
    * Reduces a collection to a single value by iteratively combining elements
    * of the collection using the provided function.
    *
@@ skipping 217 matching lines @@
  */
 abstract class BidirectionalIterator<E> implements Iterator<E> {
   /**
    * Move back to the previous element.
    *
    * Returns true and updates [current] if successful. Returns false
    * and sets [current] to null if there is no previous element.
    */
   bool movePrevious();
 }