Revert "Remove Expect from core library."

tests/language/static_implicit_closure_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 invocation of implicit closures.
 // VMOptions=
 // VMOptions=--use_slow_path
 
-import "package:expect/expect.dart";
-
 class First {
   First() {}
   static int get a {
     return 10;
   }
   static var b;
   static int foo() { return 30; }
 }
 
 class StaticImplicitClosureTest {
   static void testMain() {
     Function func = () => 20;
     Expect.equals(10, First.a);
     First.b = First.a;
     Expect.equals(10, First.b);
     First.b = func;
     Expect.equals(20, First.b());
     Function fa = First.foo;
     Expect.equals(30, fa());
   }
 }
 
 
 main() {
   StaticImplicitClosureTest.testMain();
 }