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

tools/dom/src/WrappedList.dart

Index: tools/dom/src/WrappedList.dart
diff --git a/tools/dom/src/WrappedList.dart b/tools/dom/src/WrappedList.dart
index 19c95f8ead45059437a7ec8b4449b6fd62bcf8e2..171dd7e49c8323735d4b13cfde4987b2b4ad6fa5 100644
--- a/tools/dom/src/WrappedList.dart
+++ b/tools/dom/src/WrappedList.dart
@@ -30,6 +30,9 @@ class _WrappedList<E> implements List<E> {
   dynamic reduce(initialValue, combine(previousValue, E element)) =>
       _list.reduce(initialValue, combine);
 
+  dynamic fold(initialValue, combine(previousValue, E element)) =>
+      _list.fold(initialValue, combine);
+
   bool every(bool f(E element)) => _list.every(f);
 
   String join([String separator]) => _list.join(separator);