Fix unnecessary use of this.length in ListMixin.

sdk/lib/collection/list.dart

 // Copyright (c) 2013, 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.collection;
 
 /**
  * Abstract implementation of a list.
  *
  * `ListBase` can be used as a base class for implementing the `List` interface.
@@ skipping 71 matching lines @@
   }
 
   E get single {
     if (length == 0) throw IterableElementError.noElement();
     if (length > 1) throw IterableElementError.tooMany();
     return this[0];
   }
 
   bool contains(Object element) {
     int length = this.length;
-    for (int i = 0; i < this.length; i++) {
+    for (int i = 0; i < length; i++) {
       if (this[i] == element) return true;
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     return false;
   }
 
   bool every(bool test(E element)) {
     int length = this.length;
@@ skipping 408 matching lines @@
       for (E element in iterable) {
         this[index++] = element;
       }
     }
   }
 
   Iterable<E> get reversed => new ReversedListIterable<E>(this);
 
   String toString() => IterableBase.iterableToFullString(this, '[', ']');
 }