Revert "Make EfficientLength extend Iterable."

sdk/lib/collection/splay_tree.dart

Index: sdk/lib/collection/splay_tree.dart
diff --git a/sdk/lib/collection/splay_tree.dart b/sdk/lib/collection/splay_tree.dart
index 9a41ef324d2007709f8bb7f74b65dbdca17ee7da..72a2f5293b90c4c9879b273d24afe07ed9bc9b7d 100644
--- a/sdk/lib/collection/splay_tree.dart
+++ b/sdk/lib/collection/splay_tree.dart
@@ -607,7 +607,8 @@ abstract class _SplayTreeIterator<K, T> implements Iterator<T> {
   T _getValue(_SplayTreeNode<K> node);
 }
 
-class _SplayTreeKeyIterable<K> extends EfficientLengthIterable<K> {
+class _SplayTreeKeyIterable<K> extends Iterable<K>
+                               implements EfficientLength {
   _SplayTree<K, _SplayTreeNode<K>> _tree;
   _SplayTreeKeyIterable(this._tree);
   int get length => _tree._count;
@@ -623,7 +624,8 @@ class _SplayTreeKeyIterable<K> extends EfficientLengthIterable<K> {
   }
 }
 
-class _SplayTreeValueIterable<K, V> extends EfficientLengthIterable<V> {
+class _SplayTreeValueIterable<K, V> extends Iterable<V>
+                                    implements EfficientLength {
   SplayTreeMap<K, V> _map;
   _SplayTreeValueIterable(this._map);
   int get length => _map._count;