Revert "Remove Expect from core library."

tests/language/param_test.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.
 // Dart test program for testing params.
 
-import "package:expect/expect.dart";
-
 class Helper {
   static int foo(int i) {
     var b;
     b = i + 1;
     return b;
   }
 }
 
 class ParamTest {
   static testMain() {
     Expect.equals(2, Helper.foo(1));
   }
 }
 
 
 main() {
   ParamTest.testMain();
 }