Revert "Remove Expect from core library."

tests/language/fixed_length_test.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.
 
-import "package:expect/expect.dart";
-
 // Regression test for https://code.google.com/p/dart/issues/detail?id=7994.
 
 void main() {
   Expect.equals(-1, foo());
 }
 
 int foo() {
   var list = new List<int>(1024);
 
   for(int i = 0; i < list.length; i++) list[i] = -i;
 
   for(int n = list.length; n > 1; n--) {
     for(int i = 0; i < n - 1; i++) {
       if (list[i] > list[i + 1]) {
         return list[i + 1];
       }
     }
   }
 }