Add concurrent modification check to ListMixin/IterableMixin.reduce.

sdk/lib/internal/iterable.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.
 
 part of dart._internal;
 
 /**
  * Marker interface for [Iterable] subclasses that have an efficient
  * [length] implementation.
  */
@@ skipping 157 matching lines @@
       }
       return buffer.toString();
     }
   }
 
   Iterable<E> where(bool test(E element)) => super.where(test);
 
   Iterable map(f(E element)) => new MappedListIterable(this, f);
 
   E reduce(E combine(var value, E element)) {
+    int length = this.length;
     if (length == 0) throw IterableElementError.noElement();
     E value = elementAt(0);
     for (int i = 1; i < length; i++) {
       value = combine(value, elementAt(i));
+      if (length != this.length) {
+        throw new ConcurrentModificationError(this);
+      }
+
     }
     return value;
   }
 
   fold(var initialValue, combine(var previousValue, E element)) {
     var value = initialValue;
     int length = this.length;
     for (int i = 0; i < length; i++) {
       value = combine(value, elementAt(i));
       if (length != this.length) {
@@ skipping 973 matching lines @@
  * Creates errors throw by [Iterable] when the element count is wrong.
  */
 abstract class IterableElementError {
   /** Error thrown thrown by, e.g., [Iterable.first] when there is no result. */
   static StateError noElement() => new StateError("No element");
   /** Error thrown by, e.g., [Iterable.single] if there are too many results. */
   static StateError tooMany() => new StateError("Too many elements");
   /** Error thrown by, e.g., [List.setRange] if there are too few elements. */
   static StateError tooFew() => new StateError("Too few elements");
 }