Change ListIterator to only check for concurrent modification at each iteration

tests/corelib/json_map_test.dart

 // Copyright (c) 2011, 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.
 
 library json_map_test;
 
 import "package:expect/expect.dart";
 import 'dart:convert' show JSON;
 import 'dart:collection' show LinkedHashMap, HashMap;
 
@@ skipping 144 matching lines @@
 
 void testToString() {
   Expect.equals("{}", jsonify({}).toString());
   Expect.equals("{a: 0}", jsonify({'a': 0}).toString());
 }
 
 void testConcurrentModifications() {
   void testIterate(Map map, Iterable iterable, Function f) {
     Iterator iterator = iterable.iterator;
     f(map);
-    iterator.moveNext();
+    while (iterator.moveNext());
   }
 
   void testKeys(Map map, Function f) => testIterate(map, map.keys, f);
   void testValues(Map map, Function f) => testIterate(map, map.values, f);
 
   void testForEach(Map map, Function f) {
     map.forEach((key, value) {
       f(map);
     });
   }
@@ skipping 161 matching lines @@
 }
 
 void testMutation() {
   Map map = jsonify({'a': 0});
   Expect.listEquals(['a', 0], listEach(map));
   map['a'] = 1;
   Expect.listEquals(['a', 1], listEach(map));
   map['a']++;
   Expect.listEquals(['a', 2], listEach(map));
 }