Revert "Remove Expect from core library."

tests/compiler/dart2js/unparser_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.
 
-import "package:expect/expect.dart";
 import 'dart:uri';
 import 'parser_helper.dart';
 import 'mock_compiler.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/tree/tree.dart';
 
 testUnparse(String statement) {
   Node node = parseStatement(statement);
   Expect.equals(statement, unparse(node));
 }
 
@@ skipping 341 matching lines @@
   testImport();
   testExport();
   testPart();
   testPartOf();
   testCombinators();
   testRedirectingFactoryConstructors();
   testClassDeclarations();
   testMixinApplications();
   testParameters();
 }