Move Iterable implementation to collection.

sdk/lib/collection/hash_set.dart

 // Copyright (c) 2013, 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;
 
 /** Common parts of [HashSet] and [LinkedHashSet] implementations. */
-abstract class _HashSetBase<E> extends Iterable<E> implements Set<E> {
+abstract class _HashSetBase<E> extends IterableBase<E> implements Set<E> {
   // Set.
   bool containsAll(Iterable<E> other) {
     for (E object in other) {
       if (!this.contains(object)) return false;
     }
     return true;
   }
 
   /** Create a new Set of the same type as this. */
   Set _newSet();
@@ skipping 64 matching lines @@
 
   external void removeWhere(bool test(E element));
 
   external void retainWhere(bool test(E element));
 
   external void clear();
 
   // Set.
   Set<E> _newSet() => new HashSet<E>();
 }