Move implementation from IterableBase to Iterable.

sdk/lib/_internal/compiler/js_lib/collection_patch.dart

Index: sdk/lib/_internal/compiler/js_lib/collection_patch.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/collection_patch.dart b/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
index 67e54bc0978c6367684ee3b35025e006361add9f..9242d392644fff7ec59795c0debf71fa905b9f4b 100644
--- a/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
+++ b/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
@@ -427,7 +427,7 @@ class _CustomHashMap<K, V> extends _HashMap<K, V> {
   String toString() => Maps.mapToString(this);
 }
 
-class HashMapKeyIterable<E> extends IterableBase<E>
+class HashMapKeyIterable<E> extends Iterable<E>
                             implements EfficientLength {
   final _map;
   HashMapKeyIterable(this._map);