Add Iterable.fold (and Stream.fold) which replace `reduce`.

sdk/lib/web_sql/dart2js/web_sql_dart2js.dart

Index: sdk/lib/web_sql/dart2js/web_sql_dart2js.dart
diff --git a/sdk/lib/web_sql/dart2js/web_sql_dart2js.dart b/sdk/lib/web_sql/dart2js/web_sql_dart2js.dart
index 4af5263935e7b328e51ee762ee98478df4e2cfb4..00a594735539f6dd5af79a711a6051d765bc66ac 100644
--- a/sdk/lib/web_sql/dart2js/web_sql_dart2js.dart
+++ b/sdk/lib/web_sql/dart2js/web_sql_dart2js.dart
@@ -267,6 +267,10 @@ class SqlResultSetRowList implements JavaScriptIndexingBehavior, List<Map> nativ
     return IterableMixinWorkaround.reduce(this, initialValue, combine);
   }
 
+  dynamic fold(dynamic initialValue, dynamic combine(dynamic, Map)) {
+    return IterableMixinWorkaround.fold(this, initialValue, combine);
+  }
+
   bool contains(Map element) => IterableMixinWorkaround.contains(this, element);
 
   void forEach(void f(Map element)) => IterableMixinWorkaround.forEach(this, f);