Add SplayTreeSet.

sdk/lib/core/set.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;
 
 /**
  * A collection of objects in which each object can occur only once.
  *
  * That is, for each object of the element type, the object is either considered
@@ skipping 99 matching lines @@
 
   /**
    * Returns whether this Set contains all the elements of [other].
    */
   bool containsAll(Iterable<Object> other);
 
   /**
    * Returns a new set which is the intersection between this set and [other].
    *
    * That is, the returned set contains all the elements of this `Set` that
-   * are also elements of [other].
+   * are also elements of `other` according to `other.contains`.
    */
   Set<E> intersection(Set<Object> other);
 
   /**
    * Returns a new set which contains all the elements of this set and [other].
    *
    * That is, the returned set contains all the elements of this `Set` and
    * all the elements of [other].
    */
   Set<E> union(Set<E> other);
 
   /**
    * Returns a new set with the the elements of this that are not in [other].
    *
    * That is, the returned set contains all the elements of this `Set` that
-   * are not elements of [other].
+   * are not elements of [other] according to `other.contains`.
    */
   Set<E> difference(Set<E> other);
 
   /**
    * Removes all elements in the set.
    */
   void clear();
 }