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

sdk/lib/collection/splay_tree.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;
 
 typedef bool _Predicate<T>(T value);
 
 /**
  * A node in a splay tree. It holds the sorting key and the left
@@ skipping 579 matching lines @@
   T _getValue(_SplayTreeNode node);
 }
 
 class _SplayTreeKeyIterable<K> extends IterableBase<K>
                               implements EfficientLength {
   _SplayTree<K> _tree;
   _SplayTreeKeyIterable(this._tree);
   int get length => _tree._count;
   bool get isEmpty => _tree._count == 0;
   Iterator<K> get iterator => new _SplayTreeKeyIterator<K>(_tree);
+  Set<K> toSet() {
+    SplayTreeSet<K> set =
+        new SplayTreeSet<K>(_tree._comparator, _tree._validKey);
+    set._count = _tree._count;
+    set._root = set._copyNode(_tree._root);
+    return set;
+  }
 }
 
 class _SplayTreeValueIterable<K, V> extends IterableBase<V>
                                     implements EfficientLength {
   SplayTreeMap<K, V> _map;
   _SplayTreeValueIterable(this._map);
   int get length => _map._count;
   bool get isEmpty => _map._count == 0;
   Iterator<V> get iterator => new _SplayTreeValueIterator<K, V>(_map);
 }
@@ skipping 162 matching lines @@
     return result;
   }
 
   Set<E> union(Set<E> other) {
     return _clone()..addAll(other);
   }
 
   SplayTreeSet<E> _clone() {
     var set = new SplayTreeSet<E>(_comparator, _validKey);
     set._count = _count;
-    set._root = _cloneNode(_root);
+    set._root = _copyNode(_root);
     return set;
   }
 
-  _SplayTreeNode<E> _cloneNode(_SplayTreeNode<E> node) {
+  // Copies the structure of a SplayTree into a new similar structure.
+  // Works on _SplayTreeMapNode as well, but only copies the keys,
+  _SplayTreeNode<E> _copyNode(_SplayTreeNode<E> node) {
     if (node == null) return null;
-    return new _SplayTreeNode<E>(node.key)..left = _cloneNode(node.left)
-                                          ..right = _cloneNode(node.right);
+    return new _SplayTreeNode<E>(node.key)..left = _copyNode(node.left)
+                                          ..right = _copyNode(node.right);
   }
 
   void clear() { _clear(); }
 
   Set<E> toSet() => _clone();
 
   String toString() => IterableBase.iterableToFullString(this, '{', '}');
 }