Revert "Remove Expect from core library."

tests/compiler/dart2js/dead_bailout_target_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.
 
 // This unit test of dart2js checks that a SSA bailout target
 // instruction gets removed from the graph when it's not used.
 
-import "package:expect/expect.dart";
 import 'compiler_helper.dart';
 
 String TEST = r'''
 main() {
   foo(1);
   foo([]);
 }
 
 foo(a) {
   // Make the method recursive to always enable bailouts
@@ skipping 30 matching lines @@
 
   // Check that the bailout method has a case 2 for the state, which
   // is the second bailout in foo.
   RegExp state = new RegExp('case 2:[ \n]+state0 = 0;');
   checkNumberOfMatches(state.allMatches(generated).iterator, 1);
 
   // Finally, make sure that the reason foo does not contain
   // 'getInterceptor' is not because the compiler renamed it.
   Expect.isTrue(generated.contains('getInterceptor'));
 }