Revert "Remove Expect from core library."

tests/compiler/dart2js_native/native_class_inheritance3_frog_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.
 
-import "package:expect/expect.dart";
-
 // Test to see if resolving a hidden native class's method to noSuchMethod
 // interferes with subsequent resolving of the method.  This might happen if the
 // noSuchMethod is cached on Object.prototype.
 
 class A1 native "*A1" {
 }
 
 class B1 extends A1 native "*B1" {
 }
 
@@ skipping 73 matching lines @@
 expectNoSuchMethod(action, note) {
   bool caught = false;
   try {
     action();
   } catch (ex) {
     caught = true;
     Expect.isTrue(ex is NoSuchMethodError, note);
   }
   Expect.isTrue(caught, note);
 }