Make Iterable.toSet say that it returns a Set with the same equality as the Iterable's contains met…

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;
 
 /**
  * An object that uses an [Iterator] to serve objects one at a time.
  *
  * You can iterate over all objects served by an Iterable object
@@ skipping 156 matching lines @@
    * Creates a [List] containing the elements of this [Iterable].
    *
    * The elements are in iteration order. The list is fixed-length
    * if [growable] is false.
    */
   List<E> toList({ bool growable: true });
 
   /**
    * Creates a [Set] containing the same elements as this iterable.
    *
-   * The returned `Set` will have the same `Set.length`
-   * as the `length` of this iterable,
-   * and its `Set.contains` will return the same result
-   * as the `contains` of this iterable.
-   * The order of the elements may be different.
+   * The set may contain fewer elements than the iterable,
+   * if the iterable contains the an element more than once,
+   * or it contains one or more elements that are equal.
+   * The order of the elements in the set is not guaranteed to be the same
+   * as for the iterable.
    */
   Set<E> toSet();
 
   /**
    * Returns the number of elements in [this].
    *
    * Counting all elements may be involve running through all elements and can
    * therefore be slow.
    */
   int get length;
@@ skipping 175 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();
 }