Revert "Remove Expect from core library."

tests/compiler/dart2js/concrete_type_inference_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 'compiler_helper.dart';
 import 'parser_helper.dart';
 
 void compileAndFind(String code, String name,
                     check(compiler, element)) {
   Uri uri = new Uri.fromComponents(scheme: 'source');
   var compiler = compilerFor(code, uri);
   compiler.runCompiler(uri);
   var element = findElement(compiler, name);
   return check(compiler, element);
@@ skipping 77 matching lines @@
             compiler.typesTask.getGuaranteedTypeOfElement(secondParameter));
         Expect.isNull(
             compiler.typesTask.getGuaranteedTypeOfElement(thirdParameter));
       });
 }
 
 void main() {
   testBasicTypes();
   testOptionalParameters();
 }