Revert "Remove Expect from core library."

tests/language/megamorphic_no_such_method_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.
 // Test program for correct optimizations related to types fo allocated lists.
 
-import "package:expect/expect.dart";
-
 // Classes to induce polymorphism of degree 10.
 class A0 {
   test() => 0;
 }
 
 class A1 {
   test() => 1;
 }
 
 class A2 {
@@ skipping 39 matching lines @@
   // Trigger optimization of 'test' function.
   List list = [new A0(), new A1(), new A2(), new A3(), new A4(),
                new A5(), new A6(), new A7(), new A8(), new A9()];
   for (int i = 0; i < 1000; i++) {
     for (var obj in list) {
       test(obj);
     }
   }
   Expect.throws(() => test(new B()), (e) => e is NoSuchMethodError);
 }