Revert "Remove Expect from core library."

tests/language/bailout4_test.dart

 // Copyright (c) 2012, 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";
-
 // Test that dart2s computes the right bailout environment in presence
 // of nested loops.
 
 class A {
   operator[] (index) => 42;
 }
 
 var a = new A();
 var b = new List(4);
 int count = 0;
 
 main() {
   // Make the method recursive to make sure it gets an optimized
   // version.
   if (b[0] != null) main();
 
   for (int i = 0; i < 2; i++) {
     for (int j = 0; j < 2; j++) {
       for (int k = 0; k < 2; k++) {
         Expect.equals(42, a[i + j + k]);
         count++;
       }
     }
   }
   Expect.equals(8, count);
 }