Revert "Remove Expect from core library."

tests/compiler/dart2js/class_codegen_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.
 // Test that parameters keep their names in the output.
 
-import "package:expect/expect.dart";
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
 
 const String TEST_ONE = r"""
 class A { }
 class B { }
 
 main() {
   new A();
   new B();
@@ skipping 71 matching lines @@
   String generated = compileAll(TEST_FIVE);
   Expect.isTrue(generated.contains(r"new $.A(a);"));
 }
 
 main() {
   twoClasses();
   subClass();
   fieldTest();
   constructor1();
 }