Revert "Remove Expect from core library."

tests/compiler/dart2js/compiler_helper.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 constant folding.
 
 library compiler_helper;
 
-import "package:expect/expect.dart";
 import 'dart:uri';
 export 'dart:uri' show Uri;
 
 import '../../../sdk/lib/_internal/compiler/implementation/elements/elements.dart'
        as lego;
 export '../../../sdk/lib/_internal/compiler/implementation/elements/elements.dart';
 
 import '../../../sdk/lib/_internal/compiler/implementation/js_backend/js_backend.dart'
        as js;
 
@@ skipping 153 matching lines @@
   final xRe = new RegExp('\\bx\\b');
   regexp = regexp.replaceAll(xRe, '(?:$anyIdentifier)');
   final spaceRe = new RegExp('\\s+');
   regexp = regexp.replaceAll(spaceRe, '(?:\\s*)');
   if (shouldMatch) {
     Expect.isTrue(new RegExp(regexp).hasMatch(generated));
   } else {
     Expect.isFalse(new RegExp(regexp).hasMatch(generated));
   }
 }