Revert "Remove Expect from core library."

tests/compiler/dart2js_extra/closure6_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";
-
 class A {
   var foo;
   bar() => foo(3, 99);
   gee(f) => foo(fun: f);
 
   get foo2 => foo;
   bar2() => foo2(3, 99);
   gee2(f) => foo2(fun: f);
 }
 
 main() {
   var a = new A();
   a.foo = () => 499;
   Expect.equals(499, a.foo());
   a.foo = (x, y) => x + y;
   Expect.equals(102, a.bar());
   a.foo = ({fun: null}) => fun(41);
   Expect.equals(42, a.gee((x) => x + 1));
 
   a.foo = () => 499;
   Expect.equals(499, a.foo2());
   a.foo = (x, y) => x + y;
   Expect.equals(102, a.bar2());
   a.foo = ({fun: null}) => fun(41);
   Expect.equals(42, a.gee2((x) => x + 1));
 }