Revert "Make EfficientLength public, as EfficientLengthIterable."

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 582 matching lines @@
     }
     _currentNode = _workList.removeLast();
     _findLeftMostDescendent(_currentNode.right);
     return true;
   }
 
   T _getValue(_SplayTreeNode node);
 }
 
 class _SplayTreeKeyIterable<K> extends Iterable<K>
-                               implements EfficientLengthIterable<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() {
     var setOrMap = _tree;  // Both have _comparator and _validKey.
     SplayTreeSet<K> set =
         new SplayTreeSet<K>(setOrMap._comparator, setOrMap._validKey);
     set._count = _tree._count;
     set._root = set._copyNode(_tree._root);
     return set;
   }
 }
 
 class _SplayTreeValueIterable<K, V> extends Iterable<V>
-                                    implements EfficientLengthIterable<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);
 }
 
 class _SplayTreeKeyIterator<K> extends _SplayTreeIterator<K> {
   _SplayTreeKeyIterator(_SplayTree<K> map): super(map);
   K _getValue(_SplayTreeNode node) => node.key;
@@ skipping 197 matching lines @@
     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, '{', '}');
 }