Remove Expect from core library.

runtime/tests/vm/dart/isolate_unhandled_exception_uri_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.
 
 library isolate_unhandled_exception_uri_helper;
 
+import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:isolate';
 
 // Tests that isolate code in another script keeps message handling working
 // after throwing an unhandled exception, if it has a function called
 // unhandledExceptionCallback that returns true (continue handling).
 
 // Note: this test will hang if an uncaught exception isn't handled,
 // either by an error in the callback or it returning false.
 
 void main() {
   var isolate_port = spawnUri('isolate_unhandled_exception_uri_helper.dart');
 
   // Send a message that will cause an ignorable exception to be thrown.
   Future f = isolate_port.call('throw exception');
   f.catchError((error) {
     Expect.fail("Error not expected");
   });
 
   // Verify that isolate can still handle messages.
   isolate_port.call('hi').then((value) {
     Expect.equals('hello', value);
   }, onError: (error) {
     Expect.fail("Error not expected");
   });
 
 }