Revert "Remove Expect from core library."

tests/language/library10.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.
 //
 
 library library10.dart;
 
 import "library11.dart" as lib11;
-import "package:expect/expect.dart";
 
 class Library10 {
   Library10(this.fld);
   func() {
     return 2;
   }
   var fld;
   static static_func() {
     var result = 0;
     var obj = new lib11.Library11(4);
     result = obj.fld;
     Expect.equals(4, result);
     result += obj.func();
     Expect.equals(7, result);
     result += lib11.Library11.static_func();
     Expect.equals(9, result);
     result += lib11.Library11.static_fld;
     Expect.equals(10, result);
     Expect.equals(100, lib11.top_level11);
     Expect.equals(200, lib11.top_level_func11());
     return 3;
   }
   static var static_fld = 4;
 }
 
 const int top_level10 = 10;
 top_level_func10() {
   return 20;
 }