Remove Expect from core library.

tests/benchmark_smoke/benchmark_smoke_test.dart

 // Copyright (c) 2011, 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 benchmarksmoketest;
 
 // Tests that benchmark classes used in perf testing are not broken.
 import 'benchmark_lib.dart';
 import 'dart:async';
 import 'dart:html';
+import '../../pkg/expect/lib/expect.dart';
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 
 void main() {
   useHtmlConfiguration();
 
   test('performanceTesting', () {
     Timer.run(BENCHMARK_SUITE.runBenchmarks);
     Timer.run(expectAsync0(testForCompletion));
   });
 }
 
 testForCompletion() {
   Element element = document.query('#testResultScore');
   RegExp re = new RegExp('Score: [0-9]+');
   print(element.text);
   Expect.isTrue(re.hasMatch(element.text));
 }