Revert "Remove Expect from core library."

tests/compiler/dart2js_foreign/native_no_such_method_exception4_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 'native_metadata.dart';
 
 @Native("*A")
 class A {
   bar() => 42;
   noSuchMethod(x,y) => "native($x:$y)";
 }
 
 @Native("*B")
 class B {
   baz() => 42;
 }
 
 @native makeA();
 
 @Native("""
   function A() {}
   makeA = function() { return new A; }
 """)
 setup();
 
 main() {
   setup();
   var a = makeA();
   a.bar();
   Expect.equals("native(foo:[1, 2])", a.foo(1, 2));
   Expect.equals("native(baz:[3, 4, 5])", a.baz(3, 4, 5));
 }