Make EfficientLength extend Iterable.

sdk/lib/internal/iterable.dart

Index: sdk/lib/internal/iterable.dart
diff --git a/sdk/lib/internal/iterable.dart b/sdk/lib/internal/iterable.dart
index 0e7b171e26002c4aa73f57516a1b7246196dee82..73b3669f5fc84facba92303c9b344cafd9a58313 100644
--- a/sdk/lib/internal/iterable.dart
+++ b/sdk/lib/internal/iterable.dart
@@ -8,7 +8,8 @@ part of dart._internal;
  * Marker interface for [Iterable] subclasses that have an efficient
  * [length] implementation.
  */
-abstract class EfficientLength {
+abstract class EfficientLengthIterable<T> extends Iterable<T> {
+  const EfficientLengthIterable();
   /**
    * Returns the number of elements in the iterable.
    *
@@ -24,8 +25,7 @@ abstract class EfficientLength {
  * All other methods are implemented in terms of [length] and [elementAt],
  * including [iterator].
  */
-abstract class ListIterable<E> extends Iterable<E>
-                               implements EfficientLength {
+abstract class ListIterable<E> extends EfficientLengthIterable<E> {
   int get length;
   E elementAt(int i);
 
@@ -354,7 +354,7 @@ class MappedIterable<S, T> extends Iterable<T> {
   final _Transformation<S, T> _f;
 
   factory MappedIterable(Iterable<S> iterable, T function(S value)) {
-    if (iterable is EfficientLength) {
+    if (iterable is EfficientLengthIterable) {
       return new EfficientLengthMappedIterable<S, T>(iterable, function);
     }
     return new MappedIterable<S, T>._(iterable, function);
@@ -376,7 +376,7 @@ class MappedIterable<S, T> extends Iterable<T> {
 }
 
 class EfficientLengthMappedIterable<S, T> extends MappedIterable<S, T>
-                                          implements EfficientLength {
+    implements EfficientLengthIterable<T> {
   EfficientLengthMappedIterable(Iterable<S> iterable, T function(S value))
       : super._(iterable, function);
 }
@@ -406,7 +406,7 @@ class MappedIterator<S, T> extends Iterator<T> {
  * Expects efficient `length` and `elementAt` on the source iterable.
  */
 class MappedListIterable<S, T> extends ListIterable<T>
-                               implements EfficientLength {
+                               implements EfficientLengthIterable<T> {
   final Iterable<S> _source;
   final _Transformation<S, T> _f;
 
@@ -427,7 +427,7 @@ class WhereIterable<E> extends Iterable<E> {
 
   Iterator<E> get iterator => new WhereIterator<E>(_iterable.iterator, _f);
 
-  // Specialization of [Iterable.map] to non-EfficientLength.
+  // Specialization of [Iterable.map] to non-EfficientLengthIterable.
   Iterable/*<T>*/ map/*<T>*/(/*=T*/ f(E element)) =>
      new MappedIterable<E, dynamic/*=T*/>._(this, f);
 }
@@ -500,7 +500,7 @@ class TakeIterable<E> extends Iterable<E> {
     if (takeCount is! int || takeCount < 0) {
       throw new ArgumentError(takeCount);
     }
-    if (iterable is EfficientLength) {
+    if (iterable is EfficientLengthIterable) {
       return new EfficientLengthTakeIterable<E>(iterable, takeCount);
     }
     return new TakeIterable<E>._(iterable, takeCount);
@@ -514,7 +514,7 @@ class TakeIterable<E> extends Iterable<E> {
 }
 
 class EfficientLengthTakeIterable<E> extends TakeIterable<E>
-                                     implements EfficientLength {
+                                     implements EfficientLengthIterable<E> {
   EfficientLengthTakeIterable(Iterable<E> iterable, int takeCount)
       : super._(iterable, takeCount);
 
@@ -587,7 +587,7 @@ class SkipIterable<E> extends Iterable<E> {
   final int _skipCount;
 
   factory SkipIterable(Iterable<E> iterable, int count) {
-    if (iterable is EfficientLength) {
+    if (iterable is EfficientLengthIterable) {
       return new EfficientLengthSkipIterable<E>(iterable, count);
     }
     return new SkipIterable<E>._(iterable, count);
@@ -614,7 +614,7 @@ class SkipIterable<E> extends Iterable<E> {
 }
 
 class EfficientLengthSkipIterable<E> extends SkipIterable<E>
-                                     implements EfficientLength {
+                                     implements EfficientLengthIterable<E> {
   EfficientLengthSkipIterable(Iterable<E> iterable, int skipCount)
       : super._(iterable, skipCount);
 
@@ -676,7 +676,7 @@ class SkipWhileIterator<E> extends Iterator<E> {
 /**
  * The always empty [Iterable].
  */
-class EmptyIterable<E> extends Iterable<E> implements EfficientLength {
+class EmptyIterable<E> extends EfficientLengthIterable<E> {
   const EmptyIterable();
 
   Iterator<E> get iterator => const EmptyIterator();