Revert "Change ListIterator to only check for concurrent modification at each iteration"

tests/corelib/iterable_fold_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "package:expect/expect.dart";
 import 'dart:collection';
 import 'dart:typed_data';
 
 class MyList extends ListBase {
   List list;
@@ skipping 105 matching lines @@
   testModification(base, modify, transform) {
     var iterable = transform(base);
     Expect.throws(() {
       iterable.fold(0, (x, y) {
         modify(base);
         return x + y;
       });
     }, (e) => e is ConcurrentModificationError);
   }
 
-  void add4(collection) { if (collection.length < 10) collection.add(4); }
-  void addList4(collection) { if (collection.length < 10) collection.add([4]); }
+  void add4(collection) { collection.add(4); }
   void put4(map) { map[4] = 4; }
 
   testModification([1, 2, 3], add4, id);
   testModification(new HashSet()..add(1)..add(2)..add(3), add4, id);
   testModification(new LinkedHashSet()..add(1)..add(2)..add(3), add4, id);
   testModification(new SplayTreeSet()..add(1)..add(2)..add(3), add4, id);
   testModification(new MyList([1, 2, 3]), add4, id);
 
   testModification([0, 1, 2, 3], add4, (x) => x.where((x) => x > 0));
   testModification([0, 1, 2], add4, (x) => x.map((x) => x + 1));
-  testModification([[1, 2], [3]], addList4, (x) => x.expand((x) => x));
+  testModification([[1, 2], [3]], add4, (x) => x.expand((x) => x));
   testModification([3, 2, 1], add4, (x) => x.reversed);
   testModification({1: 1, 2: 2, 3: 3}, put4, (x) => x.keys);
   testModification({1: 1, 2: 2, 3: 3}, put4, (x) => x.values);
   var hashMap = new HashMap()..[1] = 1..[2] = 2..[3] = 3;
   testModification(hashMap, put4, (x) => x.keys);
   hashMap = new HashMap()..[1] = 1..[2] = 2..[3] = 3;
   testModification(hashMap, put4, (x) => x.values);
   var splayMap = new SplayTreeMap()..[1] = 1..[2] = 2..[3] = 3;
   testModification(splayMap, put4, (x) => x.keys);
   splayMap = new SplayTreeMap()..[1] = 1..[2] = 2..[3] = 3;
   testModification(splayMap, put4, (x) => x.values);
 }