Make ListIterator throw if the underlying list's length changes.

sdk/lib/collection_dev/list.dart

Index: sdk/lib/collection_dev/list.dart
diff --git a/sdk/lib/collection_dev/list.dart b/sdk/lib/collection_dev/list.dart
index cddc75a762baf32e1a11c10c169e6481cf8cb964..34614f691c5f36e64a6085149b6529a581d79dd9 100644
--- a/sdk/lib/collection_dev/list.dart
+++ b/sdk/lib/collection_dev/list.dart
@@ -273,12 +273,17 @@ abstract class UnmodifiableListBase<E> extends ListBase<E> {
  */
 class ListIterator<E> implements Iterator<E> {
   final List<E> _list;
+  final int _initialLength;
   int _position;
   E _current;
 
-  ListIterator(List<E> list) : _list = list, _position = -1;
+  ListIterator(List<E> list)
+      : _list = list, _position = -1, _initialLength = list.length;
 
   bool moveNext() {
+    if (_list.length != _initialLength) {
+      throw new ConcurrentModificationError(_list);
+    }
     int nextPosition = _position + 1;
     if (nextPosition < _list.length) {
       _current = _list[nextPosition];