Revert "Remove Expect from core library."

tests/language/constructor8_test.dart

 // Copyright (c) 2013, 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";
-
 // Regression test for dart2js that used to crash on this program.
 
 class A {
   var b;
 
   // The parameter check here used to confuse the SSA builder when it
   // created the call to the constructor body.
   A([Map a]) : b = ?a {
     Expect.isTrue(b);
   }
 
   // The closure in the constructor body used to confuse the SSA builder
   // when it created the call to the constructor body.
   A.withClosure(Map a) {
     var c;
     var f = () { return c = 42; };
     b = f();
     Expect.equals(42, b);
     Expect.equals(42, c);
   }
 }
 
 main() {
   new A(null);
   new A({});
   new A.withClosure(null);
   new A.withClosure({});
 }