Revert "Remove Expect from core library."

tests/standalone/package/package_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.
 
 // PackageRoot=none
 
-library package_test;
+#library('package_test');
 
-import 'package:lib1.dart';
-import 'package:shared.dart';
+#import('package:lib1.dart');
+#import('package:shared.dart');
 
 void main() {
   output = 'main';
   // Call an imported lib, which will in turn call some others.
   lib1();
 
   // Make sure they were all reached successfully.
-  if (output != 'main|lib1|lib2|lib3') {
-    throw new Error("libraries were not reached successfully");
-  }
+  Expect.equals(output, 'main|lib1|lib2|lib3');
 }