Revert "Remove Expect from core library."

tests/compiler/dart2js/part_of_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.
 
 library part_of_test;
 
-import "package:expect/expect.dart";
 import 'dart:uri';
 import 'mock_compiler.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
     show MessageKind;
 
 final libraryUri = new Uri('test:library.dart');
 const String LIBRARY_SOURCE = '''
 library foo;
 part 'part.dart';
 ''';
@@ skipping 11 matching lines @@
   compiler.libraryLoader.loadLibrary(libraryUri, null, libraryUri);
   print('errors: ${compiler.errors}');
   print('warnings: ${compiler.warnings}');
   Expect.isTrue(compiler.errors.isEmpty);
   Expect.equals(1, compiler.warnings.length);
   Expect.equals(MessageKind.LIBRARY_NAME_MISMATCH,
                 compiler.warnings[0].message.kind);
   Expect.equals('foo',
       compiler.warnings[0].message.arguments['libraryName'].toString());
 }