Revert "Remove Expect from core library."

tests/language/non_const_constructor_without_body_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.
 
-import "package:expect/expect.dart";
-
 class NonConstConstructorWithoutBodyTest {
   int x;
 
   NonConstConstructorWithoutBodyTest();
   NonConstConstructorWithoutBodyTest.named();
   NonConstConstructorWithoutBodyTest.initializers() : x = 1;
   NonConstConstructorWithoutBodyTest.parameters(int x) : x = x + 1;
   NonConstConstructorWithoutBodyTest.fieldParameter(int this.x);
   NonConstConstructorWithoutBodyTest.redirection() : this.initializers();
 
   static testMain() {
     Expect.equals(null, new NonConstConstructorWithoutBodyTest().x);
     Expect.equals(null, new NonConstConstructorWithoutBodyTest.named().x);
     Expect.equals(1, new NonConstConstructorWithoutBodyTest.initializers().x);
     Expect.equals(2, new NonConstConstructorWithoutBodyTest.parameters(1).x);
     Expect.equals(
         2, new NonConstConstructorWithoutBodyTest.fieldParameter(2).x);
     Expect.equals(1, new NonConstConstructorWithoutBodyTest.redirection().x);
   }
 }
 
 main() {
   NonConstConstructorWithoutBodyTest.testMain();
 }