Add EfficientLength marker interface to some iterabels.

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 IterableBase<E> implements Set<E> {
 
   // Set.
@@ skipping 39 matching lines @@
     Set retainSet = _newSet();
     for (Object o in objectsToRetain) {
       if (isValidKey(o)) {
         retainSet.add(o);
       }
     }
     retainWhere(retainSet.contains);
   }
 
   List<E> toList({bool growable: true}) {
-    List<E> result = new List<E>()..length = this.length;
+    List<E> result = growable ? (new List<E>()..length = this.length)

[floitsch, 2013/10/10 13:04:53]

do in a separate CL.

+                              : new List<E>(this.length);
     int i = 0;
     for (E element in this) result[i++] = element;
     return result;
   }
 
   Set<E> toSet() => _newSet()..addAll(this);
 
   // TODO(zarah) Remove this, and let it be inherited by IterableBase
   String toString() => IterableMixinWorkaround.toStringIterable(this, '{', '}');
 }
@@ skipping 51 matching lines @@
   /**
    * Create a hash set containing the elements of [iterable].
    *
    * Creates a hash set as by `new HashSet<E>()` and adds each element of
    * `iterable` to this set in the order they are iterated.
    */
   factory HashSet.from(Iterable<E> iterable) {
     return new HashSet<E>()..addAll(iterable);
   }
 }