Revert "Remove Expect from core library."

tests/language/resolve_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 for testing resolving of dynamic and static calls.
 
-import "package:expect/expect.dart";
-
 class A {
   static staticCall() { return 4; }
   dynamicCall() { return 5; }
   ovrDynamicCall() { return 6; }
 }
 
 class B extends A {
   ovrDynamicCall() { return -6; }
 }
 
 class ResolveTest {
   static testMain() {
     var b = new B();
     Expect.equals(3, (b.dynamicCall() + A.staticCall() + b.ovrDynamicCall()));
   }
 }
 
 main() {
   ResolveTest.testMain();
 }