Remove Expect from core library.

tests/compiler/dart2js_foreign/native_literal_class_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("= {log: function() { return 42 } }")
 class A {
   @native void log();
 }
 
 @Native("""
   return A;
 """)
 getA();
 
 bar() {
   new A();
 }
 
 main() {
   var a = getA();
   // Make a call to bar to make sure A gets generated.
   if (a is int) bar();
   Expect.equals(42, a.log());
 }